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If the user doesn't enter a numeric value, have them keep trying

If the user doesn't enter a numeric value, have them keep trying, until they enter a numeric value

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OliveOyl3471	23 May, 2008 - 08:40 AM Post #1
It's all about the code ♥ Joined: 11 Jul, 2007 Posts: 1,606 Thanked: 17 times Dream Kudos: 150 My Contributions	I read PsychoCoder's snippet to check if a value is numeric in C#. If I had that snippet in my code, I could write: csharp if(IsNumeric(val)) { //do stuff } else { Console.WriteLine("You must enter a number. Try again.") } Could you put a while loop in there to make the user keep trying until they enter a number? csharp while(!IsNumeric(val)) { int val=Console.Readline(); if(IsNumeric(val)) { //do stuff } else { Console.WriteLine("You must enter a number. Try again."); } } would that cause an infinite loop? do I need a break; ? This post has been edited by OliveOyl3471: 23 May, 2008 - 08:43 AM
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Martyr2	RE: If The User Doesn't Enter A Numeric Value, Have Them Keep Trying 23 May, 2008 - 12:29 PM Post #2
Programming Theoretician Joined: 18 Apr, 2007 Posts: 5,173 Thanked: 208 times Expert In: C/C++, Java, VB, VB.NET, C#, PHP, Web Development, HTML & CSS, Javascript My Contributions	Well if you wanted to use a while loop you just have to set it up a slight bit differently but yeah you have the general idea. Keep in mind that Console.Readline actually returns a string, not an integer. csharp String val = Console.Readline(); while(!IsNumeric(val)) { Console.WriteLine("You must enter a number. Try again."); val=Console.Readline(); } // Do stuff here since val is numeric Now of course using something like TryParse() might be more effective in a situation like this but it is up to you. You can read about tryparse at the link below... Int32.TryParse Method on MSDN Edit: Corrected redefinition of variable. My bad. Enjoy! "At DIC we be number parsing code ninjas... we be bool ninjas = Int32.TryParse("1337",intDIC);" This post has been edited by Martyr2: 23 May, 2008 - 12:39 PM
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Jayman	RE: If The User Doesn't Enter A Numeric Value, Have Them Keep Trying 23 May, 2008 - 12:34 PM Post #3
Student of Life Joined: 26 Dec, 2005 Posts: 6,907 Thanked: 42 times Dream Kudos: 500 Expert In: C#, VB.NET, Java My Contributions	Just a minor correction to the code Martyr2 supplied. You don't want to redeclare 'val' inside the loop. CODE String val = Console.Readline(); while(!IsNumeric(val)) { Console.WriteLine("You must enter a number. Try again."); val=Console.Readline(); } // Do stuff here since val is numeric
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OliveOyl3471	RE: If The User Doesn't Enter A Numeric Value, Have Them Keep Trying 23 May, 2008 - 06:30 PM Post #4
It's all about the code ♥ Joined: 11 Jul, 2007 Posts: 1,606 Thanked: 17 times Dream Kudos: 150 My Contributions	Thank you. I wanted to use TryParse, but I didn't know how to let the user keep trying until they enter a number, til I tried it. The following code seems to work correctly. There is a switch statement where the user must enter 1, 2, or 3. Should I put a default in the switch statement? csharp int game; //if they didn't enter a number, return 0 int.TryParse(Console.ReadLine(), out game); while (game <= 0 \|\| game > 3) { Console.WriteLine("You must enter either 1, 2, or 3."); int.TryParse(Console.ReadLine(), out game); } //do stuff, since they entered a number There are several places in the program where the user is asked to input a number. Would it be more efficient to use a method such as PsychoCoder's IsNumeric() , or to keep doing it as I have done this? edit--I almost never get it right the first time. Forgot the error message, and then some other stuff. lol This post has been edited by OliveOyl3471: 23 May, 2008 - 07:08 PM
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OliveOyl3471

RE: If The User Doesn't Enter A Numeric Value, Have Them Keep Trying
23 May, 2008 - 07:19 PM

Post #5

It's all about the code ♥

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TryParse won't work for this, since sometimes the answer will be 0.

This is where I would need the IsNumeric() method...correct?

csharp


                        Console.WriteLine("Let's start subtracting!");
                        int sub1 = RandomClass.Next(1, 100);
                        int sub2 = RandomClass.Next(1, 100);
                        int trys = 0;
                        //make sure the first number is more than the second one, to avoid negative numbers
                        while (sub1 < sub2)
                        { sub1 = RandomClass.Next(1, 100);
                          sub2 = RandomClass.Next(1, 100);
                        }
                        int diff = sub1 - sub2;
                            Console.WriteLine("Subtract " + sub1 + " minus " + sub2);
                            Console.WriteLine("Type your answer now.");
                        int diffGuess = int.Parse(Console.ReadLine());//check if input is numeric

This post has been edited by OliveOyl3471: 23 May, 2008 - 07:27 PM

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OliveOyl3471	RE: If The User Doesn't Enter A Numeric Value, Have Them Keep Trying 24 May, 2008 - 09:28 PM Post #6
It's all about the code ♥ Joined: 11 Jul, 2007 Posts: 1,606 Thanked: 17 times Dream Kudos: 150 My Contributions	Instead of putting in a method for just one block of code, I changed the while loop: csharp //make sure the first number is more than the second one, to avoid negative numbers //and make sure the two numbers are not equal, so the answer will never be zero while (sub1 <= sub2) { sub1 = RandomClass.Next(1, 100); sub2 = RandomClass.Next(1, 100); } Now TryParse will work.
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