[jess64k]

I'm making a calculator that performs operations sequentially (from left to right, not precedence), using ASP.NET/C#, but I'm having trouble trying to get the loops that run through the input box in my code behind to work right.

Obviously to me the logic seems to make sense, so I can't figure out why I get a runtime error if I enter just a number and no operands, and while my error checking does work when it comes to ensuring there are no two operators together, it displays that error even when I have two or more sets of numbers and operands placed correctly between them (I.E 24+5).

I am aware its a lot of code, and while I tried to put in as many comments to explain what's going on, I believe the problem lies within my loop and how I want it to build a string until it reaches an operator or the end of the input string.

 protected void btnEquals_Click(object sender, EventArgs e)
    {
        {
            lblError.Text = "";
            if (txtResult.Text.Length > 0)
            {
                double result = 0;
                Calculator myCalculator = new Calculator();
                string input = txtResult.Text;
                string Oper = "";
                int j = 0;

                while (j < input.Length)
                {
                    string temp = "";
                    double num1 = 0;
                    double num2 = 0;
                    /* get the numbers from the input string in order until the end of string or next operator */
                    while (input.Substring(j, 1) != "+" && input.Substring(j, 1) != "-" && input.Substring(j, 1) != "*" && input.Substring(j, 1) != "/")
                    {
                        temp += input.Substring(j, 1);
                        j++;
                    }
                    num1 = Convert.ToDouble(temp);  /*create number using the built substring */

                    /*check if next part of input is an operator, and if not check if end of string*/
                    if (input.Substring(j, 1) == "+" || input.Substring(j, 1) == "-" || input.Substring(j, 1) == "*" || input.Substring(j, 1) == "/")
                    {
                        Oper = input.Substring(j, 1);
                    }
                    else if (input.Substring(j, 1) == "")
                    {
                        if (result != 0)
                        {
                            switch (Oper)
                            {
                                case "+":
                                    result = myCalculator.Add(num1, num2);
                                    break;
                                case "-":
                                    result = myCalculator.Subtract(num1, num2);
                                    break;
                                case "*":
                                    result = myCalculator.Multiply(num1, num2);
                                    break;
                                case "/":
                                    result = myCalculator.Divide(num1, num2);
                                    break;
                            }
                        }
                        txtResult.Text = result.ToString();
                        break;
                    }
                    /*check if next part of input is another operator, or end of string, and display error if true*/
                    if (input.Substring(j, 1) == "+" || input.Substring(j, 1) == "-" || input.Substring(j, 1) == "*" || input.Substring(j, 1) == "/" && input.Substring(j, 1) != "")
                    {
                        lblError.Text = "You can't have two operands next to each other or an operand without a number to its right";
                        break;
                    }

                    /* get the numbers from the input string in order until the end of string or next operator (to build second number) */
                    temp = "";
                    while (input.Substring(j, 1) != "+" && input.Substring(j, 1) != "-" && input.Substring(j, 1) != "*" && input.Substring(j, 1) != "/")
                    {
                        temp += input.Substring(j, 1);
                        j++;
                    }
                    num2 = Convert.ToDouble(temp);  /*create number using the built substring*/

                    /*perform operation using calculator class*/
                    switch (Oper)
                    {
                        case "+":
                            result = myCalculator.Add(num1, num2);
                            break;
                        case "-":
                            result = myCalculator.Subtract(num1, num2);
                            break;
                        case "*":
                            result = myCalculator.Multiply(num1, num2);
                            break;
                        case "/":
                            result = myCalculator.Divide(num1, num2);
                            break;
                    }

                    /*if an operand still exists, check if there is another operand or null after that and print error, otherwise, repeat loop*/
                    if (input.Substring(j, 1) == "+" || input.Substring(j, 1) == "-" || input.Substring(j, 1) == "*" || input.Substring(j, 1) == "/")
                    {
                        Oper = input.Substring(j, 1);
                        j++;
                    }
                    else if (input.Substring(j, 1) == "")
                    {
                        break;
                    }
                    /*check if next part of input is another operator, or end of string, and display error if true*/
                    if (input.Substring(j, 1) == "+" || input.Substring(j, 1) == "-" || input.Substring(j, 1) == "*" || input.Substring(j, 1) == "/" && input.Substring(j, 1) != "")
                    {
                        lblError.Text = "You can't have two operands next to each other or an operand without a number to its right";
                        break;
                    }
                } /*repeat loop by reading next number (WIP)*/
                txtResult.Text = result.ToString();
            }
            else
            {
                txtResult.Text = string.Empty;
                lblError.Text = "There was no input entered!";
            }
        }
    }

[andrewsw]

You get an error but you haven't told us what this error is, and what line it refers to in your posted code. Post the error!

A quick look suggests to me that you are not increment j as often as you need to.

Actually, the reverse is also true. That is, you are only checking j < input.length once at the beginning of each loop. Your code looks for a number of characters without checking whether it has reached the end of the text.

This post has been edited by andrewsw: 02 March 2013 - 06:24 PM

[tlhIn`toq]

---

tlhIn`toq's FAQ list

---

Learning to debug one's own code is an essential skill. Sadly, one that apparently few college courses teach. Silly if you ask me.

Placing breakpoints and walking through the code line by line allows you to actually WATCH it execute.

Visualizing what your code does will let you see why it behaves the way it does.

It would be well worth your time to do the tutorials on FAQ 2. A couple hours learning this skill will save you hundreds of hours of confusion in one project alone.


TOP most asked:
What does this error message mean?
FAQ 2: How do I debug
FAQ 3: How do I make Class1/Form1 talk to Class2/Form2


FAQ (Frequently Asked Questions - Updated Feb 2013

Spoiler

My program is broken:


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• Q: I do x and y happens which I didn't expect but I don't know how to figure out why. How do I debug and find my problem?
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    A condensed line like this makes a lot of assuptions that everything goes right, and gives you nothing to check or debug.
    
    If only for R&D / Debug purposes it can often be advantagous to break down the line
    

    if (dataset != null)
    {
       if (datase.Tables != null)
       {
          if (!string.IsNullOrWhiteSpace(tableName)
          {
             if (dataset.Tables[tableName].Columns != null)
    

    Now you can put a breakpoint on the top line and walk through it with F10 and check every object. You also don't try to manipulate a thing that doesn't yet exist.
  
  
  
• Q: Project ideas - Books with project ideas - What should I build next?
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• Q: ...get Form/class 'A' to make a change or talk to Form/class 'B'
  
  Spoiler

  
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  A:

  • See this thread for the simplest of example code between two forms.
    
    The tutorials below actually teach and explain it further.
    
  • Passing values between forms/classes
    
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  • Building an application - Part 2
    
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  • http://www.codeproje...g-Windows-Forms
  
  
  
• Q: ...make a binary to int calculator
  A: Read my article
  
  
• Q: ...make a tabbed web browser?
  A: Read this thread
  
  
• Q: ...make a password/login form?
  A: Password handling tutorial
  
  
• Q: ... get all the sub-folders of a folder, and the sub-folders of those, to get all the levels of directories?
  A: Its a technique known as recursion.
  
  Spoiler

  
  The GetDirectories() method will get all the directories in a folder, then call itself with those directories... which in turn get all the subfolders and calls itself with those folders... which get all the subfolders and calls itself with those folders... Recursively calling itself as it drills down.
  
  It is demonstrated on the MSDN
  http://support.microsoft.com/kb/303974
  
  
  
  
• Q: ... browse for/open a file?
  Read this tutorial
  
  
• Q: ...make a chat or client-server application?
  A:Client/server chat tutorial
  Peer-to-peer chat
  
  
• Q: ... get my program to programmatically simulate a mouse click or button press?
  A: Simulate mouse and keystroke (even to another application)
  
  
• Q: ... save data, save properties, save environmental variables, serialize my data/class?
  A:
  Spoiler

  • Separating data from GUI - PLUS - serializing the data to XML
    
  • Working with environmental variables
    
  • Writing a text file tutorial.
    
  • Reading a text file tutorial.
    
  • Easy Application Settings example
  
  
  
• Q:... get sound in my program?
  A: Adding sound to your C# application
  
  
• Q: ... use the serial port?
  A: Serial port communication
  
  
• Q: ...do compression or .zip files?
  A:
  • (de)Compression tutorial
    
  • Zip files tutorial
  
  
  
  
  
• Q:Make a progress bar work on its own thread to show progress to the user while work is being done?
  A: Background worker tutorial
  
  
  
  
  
• Q:...do multi-threading? Having a problem with cross-threading...
  
  Spoiler

  A:

  • Cross thread calls tutorial
    
  • How to use a thread pool.
    
  • Decouple your multi-threaded work from the GUI so forms don't hang
    
  • thread synchonization
    
  • Advanced threading
    
  • MSDN asynch communication
  
  
  
• Q: ...Why my multi-thread throws a cross-threading error when it tries to update my GUI?
  A: Your thread shouldn't be trying to affect any GUI at all: Ever.
  
  Spoiler

  
  

  Quote

  But when I kick off the background worker and it goes to change a label in this panel

  
  
  I'll stop you right there. That underlying principal for your program is the problem and just won't work. The worker is a different thread than the one that created the GUI.
  
  Background threads do not, ever, directly access anything that they didn't make. Period. Accept that and start re-designing.
  
  Background worker raises events. You main class that makes this background worker has to subscribe to those events. Then that thread can update its GUI.
  
  This is how is it meant to work. Each 'thing' in a program really should have only one purpose in life and cause no side affects. The background worker should do its job and nothing else. Its job is not to manage the GUI. The GUI thread's job is to manage the GUI.
  
  Think of it this way: Your car dashboard has one job: To be the GUI for your car. But if the speedometer dies you don't want that to keep the engine from starting. The speedometer and the engine are 'loosely bound' for a reason. Your program is the same. You need the GUI to run whether or not the background worker does, and you want the background worker to run regardless which GUI you have on display.
  
  So the background worker is kept ignorant of which panel you have up. It just says "I'm 50% done". If you have the simple panel or the complex panel on display doesn't matter. It hears the event and does whatever it is designed to do to display those results. Maybe the simple panel uses a progress bar, while the advanced panel display the exact percentage. The background thread doesn't know or care how it is shown.
  
  

  Quote

  So my main application should make a dozen threads to update the dozen similar controls?

  
  
  To me that sounds like the main application is doing too much work and micromanaging the other controls. If the main application is coded for 12 background threads and panels, what happens in 6 months when you want to add a couple more panels? You have to update all your infrastructure to support them.
  
  Personally I would make UserControls that consist of the Panel, its own backgroundworker and any pure objects that you might want to serialize for later restoration. The idea is to make a complete and fully self-contained 'Lego Block' of functionality. Then use your application to just hook them all together.
  
  Now you can place 2 of your custom controls on screen... or 20... and they each take complete care of themselves. Only when one of your custom controls raises an event like LogThis(string message) or HighLevelWarning(int level) does the application have to do anything. The bulk of the work is done within the UserControl
  
  In each of these UserControls I would create methods for Start() and Stop(). Let the UserControl handle its own needs.
  
  Your main application should do nothing more than:
  
  

  StartAllPanels()
  {
     foreach(CustomPanel cp in myPanelsCollection)
     {
        cp.Start(); // Tell the panel to start
        cp.WarningMessage += WarningHandlerMethod; // Subscribe to warning event
        cp.LogThis += LogMessageHandlerMethod; // Subscribe to logging event
     }
  }
  

  
  
  See how your main application has no idea what the panel needs to do to start up? It doesn't try to micromanage the panel and tell it to start it's backgroundworker. The main app is blissfully ignorant of the inner needs of the component. Its like a the driver of a car. The driver doesn't tell the car: Close 12v power, start fuel pump, begin ignition computer, calibrate fuel/air mix, confirm foot is on brake, start ignition... The driver just turns the key to Start(). Your application should be the same. It only needs to know what it NEEDS to know. Let the rest of the parts take on as much responsibility as you can push on them.
  
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  The tutorials below walk through making an application including inheritance, custom events and custom controls, object serialization and more.
  Quick and easy custom events
  Bulding an application - Part 1
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  Separating data from GUI - PLUS - serializing the data to XML
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  Passing values between forms/classes
  Decouple your multi-threaded work from the GUI so forms don't hang
  
  
  
  
• Q: ... make my textbox offer suggestions as the user types. (Autocomplete)
  A: Creating an auto-complete textbox
  
  
• Q: ... make a textbox just accept numbers and not letters?
  A: Read this thread
  
• Q:I get an error when I try to use a textbox for numeric values and the user types non-numbers. What do I do?
  A:
  Spoiler

  We see this a LOT, especially with rookies using textbox for numeric input.
  
  Any input that can't be converted to a number will do this.
  "5" can become 5
  "yogi" cannot become a number
  string.empty cannot become a number
  
  You would be best off changing from a textbox to a NumericUpDown or to inherit from textbox to make a numerictextbox.
  
  There are a LOT of articles on making a NumericTextBox. Try googling "C# NumericTextBox" and you should find a lot, such as this one on the MSDN:
  http://msdn.microsof...4(v=vs.80).aspx
  
  Once you study the code you'll see that as each key is pressed it is checked to see if it is a number. If not, then it is ignored. Thus the user can only enter numerically valid values.
  
  
  
• Q: ... use PInvoke and the Win32 api calls to get functions not available in .NET framework?
  A: Using the Win32 API Tutorial
  
  
• Q: ... have both a WinForms Windows app, and still have a Console window open?
  
  Spoiler

  A: Make your new project a WinForms project. Then go back to project properties (Right-click on the project, select Properties).
  
  On the Application tab go to the dropdown that says "Windows Forms" and change it to "Console Application." You now have a WinForms application with a console window. I do this on occassion to see my Console.WriteLine statements when I am debugging. But don't consider this mixed mode operation a proper way to release an application for real-world use.
  
  
  
• Q: ... make a username/password logon (login) system?
  A: Read this tutorial
  
  
• Q: ... make global hotkeys?
  A: Global Hotkeys Tutorial
  
  
• Q: ...deal with ',' and '.' being swapped in numbers in some countries?
  A: So you live in a country where "." is the seperator for thousands and "," is the separator for whole and fractional (the decimal point)?
  
  Rather than change your region settings, and expect all the users of your software to do as well, you should fix the bug.
  
  NumberFormatInfo
  Globalization of numbers
  Parsing numeric strings
  
  
  
  
  
  Can someone explain...
  
  
• Q: ... I have these two arrays. One is strings like someone's name and the other is numbers like ages or test scores. How do I keep the two in synch? I want to be able to sort the names and keep the ages/scores binded to the names.
  A: Moving away from Parallel arrays - SUPER tutorial.
  
  
  
  
• Q: What are lambdas? What Is (Obj, E) => ?
  A: Excellent article by Curtis Rutland
  
  
• Q: ... how to do x, y, z with the HTML that comes out of a website ...
  A: Check out the HTML Agility Pack. Yes its free.
  
  
• Q:... how to do x,y,z with a database {probably for the first time}...
  A: Read this tutorial
  Entire section of tutorials
  Parameterizing Your SQL Queries: The RIGHT Way To Query A Database.
  Using SqlDependency to monitor SQL database changes
  
  
• Q: Can someone explain bitwise operations?
  A: Terrific explanation by CodingSup3rnatur@l-360. Be sure to +1 him for this thread.
  
  
  I'm lost while learning xyz... I don't know where to begin...
  
  
• Q:I'm trying to teach myself programming. I'm writing a program to do xyz, rather than following a guided self teaching book or lesson plan or on-line tutorial because I just don't learn from books.
  A:
  Spoiler

  I'm sorry for how this sounds. I tend to take the stance that I can do you more good and give you more long-term meaningful help by being frank and give you adult-level honesty. I don't feel it does anyone any good to coddle them and do nothing but blow sunshine and rainbows up their skirt. I'd rather say something
  to motivate you than feel my place is to bolster your false high self esteem.
  
  

  Quote

  ]
  I've tried going through those, the only way im learning is through struggling to write code from scratch, the thought process i guess is helping me, i've tried reading sooo much and watching videos but honestly I'm not learning until I actaully type it.

  
  
  I hear this a lot and the only thing I can think is students are buying the wrong books. Or they read the information and don't feel they need to actually work the lessons/exercises. This argument sounds like there are only two choices:
  

  • Develop from scratch even though they haven't learned the language yet.
    
  • Just read C# dictionaries.

  
  
  Maybe this is from students buying the course textbook and reading it on their own, without the benefit of the teacher and their lesson plan and exercise assignments. When one mis-uses the materials, or only has 25% of the materials, of course they won't learn.
  
  Here's a tip when selecting a book: If it is a dictionary of the language it is not a teaching book. Titles like "C# 4.0, The Complete Language" are not teaching books. If the title includes the words "Learn" or "Master" or "Teach" they might be teaching books. "Learn C# in 21 days", "Master C# in 2 hours a night", "Head First C#, A self-teaching guide" Then they are probably teaching books with a lesson plan and exercises to help you build up skills.
  
  Obviously you didn't read the resources list I posted or get any one of the NUMEROUS self-teaching books.
  
  Self-teaching books HAVE YOU TYPING CODE. They are NOT just reading as you describe.
  
  C# is a language just like Russian or English. You cannot learn Italian by just reading an Italian dictionary.
  
  Or even reading an English-to-Italian dictionary. You have to take lessons and do the learning exercises. Those lessons and exercises are developed by professionals to take place in a sequence proven to work, by taking the student from simple to complex concepts. You did not learn how to compose literary works in English by just reading a dictionary. You worked at lessons that taught you the syntactical use of verbs, nouns, additives and so on. You worked lessons that had you build simple things first like "Those are my apples. These are your pencils", and worked up from there.
  
  So why are you trying to "just read" to learn C#? Or why are you insisting on trying to design and code a working program without first learning the language? It makes no sense! Its like saying you have to design and write a mystery novel as your introductory educational process to learn German. Its just a fraking ridiculous argument to try to take or defend.
  
  There are numerous on-line learning series on the internet that have you learning and WRITING code, not just reading. We have them right here on DIC and they have been linked to you several times. There are many good guided self-teaching books, that once again are NOT just reading but teaching through proven methods of:
  

  • Introduce new material
    
  • Have student exercise with new material

  
  
  Yet you insist that you don't need to go the route that has worked for the 3 generation of coders before you:
  
  Representatives of which are here TELLING you that is the way to learn this science/skill/art.
  
  

  Quote

  would i be able to take out the private double[] months = new double[12];
  and place it in a method instead of leaving it in a private field, why does it have to be in a private field as opposed to a method in just placing it in the main method?

  
  
  Questions like this last one show just how badly you need to stop trying to write this program and just concentrate on learning the language through some sort of guided lesson plan. This question is filled with so much lack of understanding that it is hard to know where to start in an effort to answer it. To answer this someone would have to back up 5 chapters and help you get a grasp of certain introductory concepts. It's not right to ask that of people that have already devoted tens or hundreds of hours to develop the tutorials we have here. You shouldn't be asking them to repeat themselves because you feel you need special hand-holding or because you don't want to get the right books or because you don't want to actually work the exercises in the books or tutorials.
  
  
  
  
  
• Q: I'm making a maze generator/solver and...
  A: http://www.codeproje...enerator-Solver
  
  
  
• Q: I am making a calculator as my school homework project and ...
  A: Calculator tutorial
  
  
• Q: I've been struggling with this for days/weeks and I can't figure it out and my professor is worthless and can't teach. Can someone here explain it to me?
  A:
  Spoiler

  If you are struggling with how to do this you need to talk to your professor. Let him/her know you are struggling at this early stage in class. Make your professor do the job (s)he gets paid to do by either helping you or finding you a tutor or giving you more exercises from earlier in the book. You are paying for this education. Be an active part in not allowing the teacher to brush you off and let you slip through the cracks. If the other 50 people in class aren't struggling then don't blame the teacher. If the other 50 people are struggling then you all need to go to the professor's superior and tell him/her. If the prof is really incompetent then you don't need to help him keep his cushy 100,000/year job. If the prof isn't incompetent then you need to study harder or consider buying another book on programming. You aren't required to ONLY use the text book provided for the class.
  "How do you resolve your issues" survey.
  
  
  
  
• Q: I am doing a dice game for a school homework and...
  A:Drawing dice on the console
  
  
  
  
• Q:

  Quote

  Hi,I'm currently learning C# in class at the moment and I'm a little bit stuck on what this question means.[...]show me where I can get help,
  
  A:
  Spoiler

  Your professor. That's where to start for a couple reasons:
  1. They are getting paid to teach you. If they aren't teaching you this needs to come to their attention and that of their superiors.
  2. You're the one paying them. Tens of thousands of dollars for your education. You need to learn to take every ounce of knowledge you can from these teachers and not sit passively back and try to learn it on the outside. If you were going to do that then you didn't need to take out all the student loans that are going to keep you in
  
  debt for the next 15 years.
  3. You need to let the teacher do their job. If you are struggling here you don't want to hide it. You need them to be aware of position so they can give you the time and attention you need. Otherwise you will be a little lost on chapter 1. A little more on 2. Way behind by chapter 3. You have to get a good foundation now if you are to gain anything in the later lessons.
  
  
  
• Q: I want to write a program that does x, y and z with features for A, B, and C. {Notice there is no question in this question}
  A:
  Spoiler

  That is a very good statement of intent. Go right ahead. You don't need to announce your intentions to us, nor get anyone's permission. After you have made an effort to your own code (in good faith as described in the Welcome DIC email you got when you joined) and the forum rules that I'm sure you read before posting, and you have a QUESTION about this project... Please post the QUESTION here in this same thread.
  
  There is no need to start a new thread for this same topic.
  
  
  
• Q: I need to code to do x... Someone tell me the code for y...
  A:
  Spoiler

  Your question is about to get bounced for begging for code anyway but...
  So you're asking the volunteers here to write your code for you, to make it do everything in your wish list?
  
  Please read the rules.
  
  You seem to misunderstand what we do here. We help people learn to code. We help people with their projects. We help people better understand the errors and exceptions they are getting so they can fix their issues. We are not a free code writing service. If you have made an effort to code a specific feature, but are not getting the results you wanted then please post the relivant code for that feature along with the error messages or an explanation of what results you are seeing as compared to the results you were expecting, and we will try to guide you onto the right path.
  Read this article!!!!!
  
  
  
  
  Discussion topics:
  
  
• Q: What is the best programming language/OS? What programming language/OS should I learn?
  A:
  Spoiler

  All of them. And none of them. You might as well be asking "What is the best kind of vehicle?" Because the answer for both questions is "It depends on your needs and what personally suites you the best." C, C++, C#, Objective-C, Cocoa, F#, Visual Basic, Python, JAVA...
  
  Are all good languages. They all have their pros and cons. They each have their strengths and weaknesses. Some have stronger footholds in some markets than others. Do you want to write for iPhone/iPad then you need Objective-C. Do you want to write for generic mobile phone use then you need JAVA. And so on. If you have no idea what area of programming you want to move to (Gaming, Financial, Windows, Macintosh, Cell phones) then nobody can advise you on a language. Personally, I would point you to C# because, like it or not, Microsoft owns the desktop computer market and C# will teach you good habits of design, OOP (Object Oriented Programming) design, inheritance and so on: Concepts that translate well to all other OOP languages.
  
  The OS is a by-product of the type of coding you want to do, which in turn dictates the language you need, which then decides the operating system you probably need. Not the other way around.
  
  Do you want to code apps for iOS devices like the iPad and iPhone? Then you need a Macintosh to do it right. Are you hankering to do machine vision programming? Industrial robot control? Financial applications?
  
  What are your programming goals? Do you want to market $9.99 desktop applications to the masses? Do you want to make control systems for helicopters? XBox games requires the .NET XNA framework so you are now in Windows. Do you want to do embedded controls for automotive computers? Do you just love MS Office and love to make extensions for it? Do you want to work on web apps or desktop apps or mobile apps?
  
  Do you now see why we can't even begin to tell you what is best for you? Only you know what you like and what you don't like. Only you know what area of programming is interesting to you. If you ask me for advice I might tell you video processing for the movie industry is great so you should get a Mac. Someone else is going to tell you cool stories of working on CSI lab equipment so you should do C embedded stuff.
  
  The short answer for this question is: Get in touch with your own wants and needs then think for yourself.
  
  Join these discussions on the topic:
  Which coding language?
  VB6 is dead
  C# or C++?
  
  
  
  
• Q: What language should I learn so I can be employable in the future? What's the future of software engineering? What should I study so I can be successful working at home?
  A:
  Spoiler

  Yeah, you're sparking a "Which language is best?" war.
  
  This has been covered so many times here. The short answer is:
  
  They are all good, and they are all bad. You need the right tool for the job. You don't build desktop application in HTML. You have to decide what area of programming you want to do. You talk about "contract work" like it is all the same. That's like saying "Plastics". There are 100,000 different kinds. If you want to code for Xbox games you use a different language and IDE than you do for iPad games. So you need to pick an area of coding you want to work in, then determine what tools are used for that.
  
  As for the questions about "what will be useful in the future?"... We aren't fortune tellers. If we had a crystal ball that told us the future of computing software engineers wouldn't be in the unemployment lines along side welders. And if the senior developers looking for work had that crystal ball, frankly they wouldn't be telling kids fresh out of school what areas to go to so as to create even more competition for those rare jobs.
  
  I think you need to recognize the that software engineering is a job in the real world just like any other. People compete. 1,000 applicants apply for 1 job. That's the real world.
  
  If you want to compete on oDesk, great. Then actually LOOK at oDesk for the desired skills rather than ask us. What contracts are being offered? What technologies are being asked for? What is the pay rate for those gigs? Can you build a system fast enough to make a living at it? Because here's what I notice there most of the time: Someone wants you to build an entire Point of Sale system from inventory to sales counter software, with barcode reader integration and full on-line ecommerce store. The maximum pay is $500. If you can build all of that in 10 hours then you are making $50/hour or around $100k/year. Which is what you need to make considering you are freelance and have to pay your income taxes and social security out of that since you are now your employer. If you can build all of that in 10 hours: Wow! If it takes you 100 hours (2.5 work weeks is still pretty quick) then you are making $5/hour. Can you feed your family on that? Not if you live in a first world country. Maybe if you live in Mumbai.
  
  
  
• Q: How do I become a programmer?
  A: Click the link
  
  
• Q: I'm not really sure what I want to do with my future? Do you guys like programming? I think I kinda like math and games and computers? What should I do or study?
  A:
  Spoiler

  
  You are asking a very vague, generalize question about a broad topic.
  You might as well be asking... What is the best kind of vehicle to buy? Or what is the best kind of plastic to make? It all depends on your needs... Your area of business.
  
  If you are interested in embedded devices like computers that control automobile engines it is still programming - but it is entirely different to writing a point of sale program meant to be used as a self-service kiosk like you see at Home Depot. And that is entirely different to writing a program that is meant to be used on a mobile platform.
  
  You need to make a decision about what kind of programming, what area of interest, what industry you want to work in, before you can worry about the specifics of which language and OS and platform.
  Which Language Should I Learn?
  DIC Tutorials Section
  Good thread on the topic
  Get experience while you find yourself
  
  
  
• Q: What's your installation like? What sofware do you use? What are your Visual Studio extensions?
  A:
  Spoiler

  
  

  • Host Operating System - 16gig, quadcore, 3x24" Dell LCDs at 1920x1200 (2 landscape, 1 portrait)
    
    • 20 times of on-line update/reboot cycle
      
    • Device Drivers
    • AVG antivirus
      
    • VMware workstation
    
    
    • VM Operating System
      
      • 20 times of on-line update/reboot cycle
        
      • Device Drivers
        
      • Visual Studio
        
        • ReSharper
          
        • Dotfuscator
          
        • CodeMaid
          
        • XAML regions
          
        • XAML code cleanup
          
        • InstallShield
        
        
      • Expression blend studio
        
      • MS Office
        
      • SnagIt
        
      • Safari
        
      • iTunes
        
      • Fences
        
      • Yahoo messenger
        
      • FoxIt PDF reader
        
      • AnyDVD (I have DVDs from 3 different regions)
        
      • TightVNC
        
      • Dropbox
        
      • AVG anti-virus
        
      • Quicken
        
      • Canon RAW codec
        
      • Shark007 codec pack for Media Center
        
      • Another 20 rounds of on-line update/reboot
        
      • Take a snapshot of the VM machine for easy restoration

  
  
  That is my entire install
  
  
  
  
  
  
  Working for myself/Deploying/Selling software:
  
  
• So you want to be a game programmer...
  
  
• Q:How do I stay a free lance coder for a living?
  A:http://justcreatived...eelancing-life/
  
  
• Q: How do I become a better coder?
  Read this, and practice a lot.
  How to be a better coder
  
  
• Q: Are there any resources for small C# projects a novice to become a better coder?
  A:
  Spoiler

  There is a novice projects thread here on DIC. But here's my advice whenever this comes up:
  
  Look around. Anyone who can't find a dozen projects a day by just walking through life, is doing so with their eyes closed to the world.
  

  • Do you like the weather? What about a program to get the various weather reports from different web sites?
    
    Or to integrate with one of the numerous USB weather station hobby kits on the market?
    
  • Do you like the run? What about a program to log your runs, routes and progress?
    
  • Do you like movies? What about a program to catalog all your DVD's and AVI's?
    
  • Do you like photography? What about a program to browse your images, assign tags and GPS?
    
  • Do you like shooting? What about a program to track your aim and improvement?
    
  • What about every time you walk into a business and someone says "Oh, I'm sorry. The computers are slow/suck.
    
    This is going to take 10 minutes and 25 screens." Sounds like an opportunity to make and maybe even sell them a new program. So go home and make it first before you open your mouth. If you succeed in something great. If you fail, then you know where to study more and you haven't embarrassed yourself.

  
  
  What about every time you walk into a business and someone says "Oh, I'm sorry. The computers are slow/suck. This is going to take 10 minutes and 25 screens." Sounds like an opportunity to make and maybe even sell them a new program. So go home and make it first before you open your mouth.
  
  If you succeed in something great. If you fail, then you know where to study more and you haven't embarrassed yourself.
  
  Go to any of the on-line coder for hire sites. Read the new contract descriptions. DON'T BID ON THEM. Just read them. This will tell you what is requested by employers so you know where you have the potential to make money, and tell you where you should study. Then pick a project and build it. TRACK YOUR TIME. If you don't know how
  
  long it takes you to build a project then you won't be able to bid on contracts. If you bid $50 for 50 hours of work you're going to starve to death. Again, building projects just to learn the technology and learn your own speed and weaknesses is something we all do/did and you need to do too. Once you can build a project just for the learning experience, fast enough that you could have made a competitive bid... Now you can start considering actually bidding on new contracts that are in your skill set.
  
  
  
  
• Q: How do I sell the software I've developed?
  A:http://www.dreaminco...m_notifications
  
  
• Q: How do I decide how much to charge for my application?
  A: Read this
  A lot of questions about freelancing were covered in the Q&A with the Experts thread
  
  
• Q: How do I deploy my program / Make an installer?
  A: C# application deployment project
  Include the smallest .NET possible

---

[andrewsw]

You are over-complicating this. I would consider something like:

    string sample = "34*8+5";
    string tempNum = "";
    List<string> parsed = new List<string>();

    foreach (char item in sample) {
        if (char.IsDigit(item) || item == '.') {
            tempNum += item;
        } else {
            parsed.Add(tempNum);
            tempNum = "";
            parsed.Add(item.ToString());     // operator
        }
    }
    if (tempNum != "") {
        // we should be left with one more number
        parsed.Add(tempNum);
    }
    string display = "";
    foreach (string item in parsed) {
        display += item + ", ";
    }
    display = display.TrimEnd(',', ' ');
    MessageBox.Show(display);

It needs additional checks to make sure the first item is a number, and to disallow consecutive operators, etc., but will still be much easier to manage than your currrent code.

This post has been edited by andrewsw: 02 March 2013 - 07:03 PM

[andrewsw]

Once you've collected the various bits in parsed you can loop through this again (having checked that it is valid) to perform your calculations.

[andrewsw]

I don't need the foreach, I/we can just use Join():

    string display = "";
    //foreach (string item in parsed) {
    //    display += item + ", ";
    //}
    display = String.Join(",", parsed);

    //display = display.TrimEnd(',', ' ');
    MessageBox.Show(display);

[jess64k]

andrewsw, on 02 March 2013 - 07:02 PM, said:

You are over-complicating this. I would consider something like:

    string sample = "34*8+5";
    string tempNum = "";
    List<string> parsed = new List<string>();

    foreach (char item in sample) {
        if (char.IsDigit(item) || item == '.') {
            tempNum += item;
        } else {
            parsed.Add(tempNum);
            tempNum = "";
            parsed.Add(item.ToString());     // operator
        }
    }
    if (tempNum != "") {
        // we should be left with one more number
        parsed.Add(tempNum);
    }
    string display = "";
    foreach (string item in parsed) {
        display += item + ", ";
    }
    display = display.TrimEnd(',', ' ');
    MessageBox.Show(display);

It needs additional checks to make sure the first item is a number, and to disallow consecutive operators, etc., but will still be much easier to manage than your currrent code.

Sorry for not mentioning the error message, its my first time posting a code question!

The error I get when hitting the equals button when there is nothing or numbers without any operand in the string is:

System.ArgumentOutOfRangeException: Index and length must refer to a location within the string.
Parameter name: length

I had a strong feeling I was over complicating things. As tlhIn`toq mentioned, college classes do skip over the debugging feature of coding environments, and I hate to admit that mine is no exception, even moreso because our curriculum has us learning VB as a prereq then has us jump into C# without any knowledge of its functions :\

Thank you for the code example though, I will try it out and post back if I have any questions, if the help is willing

[jess64k]

Here is what I have so far. Its not displaying an error, and works if there are two numbers and an operand only in the input box. What's odd is that any more than that (I.E 2+4+5) and my "consecutive operators" error kicks in and despite my code to break the loop, it still does the math for the first two numbers and operator of that string (so 6 in the example).

I THINK the problem might be that certain variables are begin carried over into the next iteration of the loop, but I'm not quite sure. Any help would be much appreciated! Apologies in advance if I butchered your initial code Andrew and its intended direction.

 protected void btnEquals_Click(object sender, EventArgs e)
    {
        lblError.Text = "";
        if (txtResult.Text.Length > 0)
        {
            string input = txtResult.Text;
            string temp = "";     
            Calculator myCalculator = new Calculator();
            List<string> parsed = new List<string>();

            foreach (char item in input)
            {
                if (char.IsDigit(item) || item == '.')
                {
                    temp += item;  //number
                }
                else
                {
                    parsed.Add(temp);
                    temp = "";
                    parsed.Add(item.ToString());     // operator
                }
            }
            if (temp != "")
            {
                //we should be left with one more number, gets grabbed here
                parsed.Add(temp);
            }
           // string display = "";
            double num = 0;
            double num1 = 0;
            double num2 = 0;
            string Oper = "";

            foreach (string item in parsed) //do check/calc in here. Each 'item' is a set of numbers, or an operand
            {             
               if (double.TryParse(item, out num)) //check if item is a number
                {
                    if (num1 == 0) //if the first number isn't taken of the operation isn't taken, assign it
                    {
                        num1 = num;
                    }
                    else if (num2 == 0)//otherwise, make it the second number of the operation
                    {
                        num2 = num;
                    }
                }
                else //if its not a number, its an operand
                {
                    if (Oper != "") //check for consecutive operator, error if true
                    {
                        lblError.Text = "ERROR: You cannot have consecutive operators!";
                        break;
                    }
                   Oper = item;
                }
                //check for divide by 0, error if true
                if (Oper == "/" && num2 == 0)
                {
                    lblError.Text = "ERROR: Cannot divide by 0!";
                    break;
                }
               else if (Oper != "" && num2 != 0) //if there is a second number and an operand, perform a calculation
                {
                    double result = 0;
                    switch (Oper)
                    {
                        case "+":
                            result = myCalculator.Add(num1, num2);
                            break;
                        case "-":
                            result = myCalculator.Subtract(num1, num2);
                            break;
                        case "*":
                            result = myCalculator.Multiply(num1, num2);
                            break;
                        case "/":
                            result = myCalculator.Divide(num1, num2);
                            break;
                    }
                    txtResult.Text = result.ToString(); //output results to textbox          
                }
            } //repeat for next set of operations  
        }
        else
        {
            txtResult.Text = string.Empty;
            lblError.Text = "There is no input entered!";
        }
    }

[andrewsw]

As suggested by tlhIn`toq you need to learn how to debug your code. There is a tutorial link in my signature. But you also need to make sure that your algorithm - your solution - will work, perhaps using pen and paper

I would probably use a for loop, looking at pairs of elements:

for (int i=0; i < parsed.Count-1; i = i+2)

I think you are concentrating too much on error checking. I would get it to work first! Convince yourself that it will work (with valid input) by testing it. Then gradually introduce error checking with a few if statements, using return; if an error is found, so that no further processing occurs.

The error checking should be fairly straight-forward:

Quote

Are there an odd number of elements?
Is every second (odd) element a valid number?
Is every middle element a valid operator? That is, is it in "+-*/"?

I would deal with division by zero a bit later, as it is a little more fiddly to determine.

This post has been edited by andrewsw: 03 March 2013 - 04:36 AM

[andrewsw]

The following seems to work, although I haven't tested it thoroughly:

    string sample = "30+2*2-5";
    string validOps = "+-*/";
    string tempNum = "";
    double tempDbl;
    List<string> parsed = new List<string>();

    foreach (char item in sample) {
        if (char.IsDigit(item) || item == '.') {
            tempNum += item;
        } else {
            parsed.Add(tempNum);
            if (Double.TryParse(parsed.Last(), out tempDbl)) {
                // do nothing..
            } else {
                MessageBox.Show("Not a number");
                return;
            }
            tempNum = "";
            parsed.Add(item.ToString());     // operator
            if ( validOps.Contains(item.ToString()) ) {
                // it's an operator, do nothing..
            } else {
                MessageBox.Show("Not a valid operator");
                return;
            }
        }
    }
    if (tempNum != "") {
        parsed.Add(tempNum);
    } else {
        MessageBox.Show("You didn't end with a number");
        return;
    }
    if (parsed.Count % 2 == 0) {
        MessageBox.Show("There should be an odd number of elements");
        return;
    }
    string display = "";
    display = String.Join(",", parsed);
    MessageBox.Show(display);

    double result = 0.0, num = 0.0;
    char oper = '\0';
    for (int i = 0; i < parsed.Count; i = i + 2) {
        if (i > 0) {
            num = Double.Parse(parsed[i]);
            switch (oper) {
                case '+':
                    result += num;
                    break;
                case '-':
                    result -= num;
                    break;
                case '*':
                    result *= num;
                    break;
                case '/':
                    if (num == 0.0) {
                        MessageBox.Show("Cannot divide by zero");
                        return;
                    }
                    result /= num;
                    break;
                default:
                    // do nothing
                    break;
            }
        } else {
            result = Double.Parse(parsed[i]);
        }
        if (i < parsed.Count - 1) {
            oper = Char.Parse(parsed[i + 1]);
        }
    }
    MessageBox.Show(String.Format("result is {0}", result));
}

but, of course, you would need to study, and adapt it, to make use of it with your myCalculator object.

[andrewsw]

I also need an extra check, checking that the last value is actually a number:

    if (tempNum != "") {
        if (Double.TryParse(tempNum, out tempDbl)) {
            // do nothing..
        } else {
            MessageBox.Show("Didn't end with a number");
            return;
        }
        parsed.Add(tempNum);
    } else {

[Skydiver]

I suspect that part of the issue that our OP is having to contend with is the difficulty of debugging ASP.NET applications. The edit-compile-run cycle is much slower and there is more opportunities to lose focus between those transitions.

I highly recommend starting a small Console program that just has a hard coded string, and try working out the core of your algorithm first. The edit-compile-run cycle is much tighter and you don't have to fight with the vagaries of either IIS or the Development Web Server. Once you have your code working, transplant the core back into your ASP.NET program.