this is an exercise in our structures class (i'm actually a week late, T_T)

the exercise is to make a parsing program using stacks, with the push, pop, and stacktop functions being put in a separate c file, to be accessed using #include (i'm not sure how to do that since it didn't work when i attempted it, so for now i put it together with my main function.)

my basic algo:

1. get the expression
2. ignore all elements that aren't '(' or ')'
3. if it's '(', i push it into the stack
4. if it's ')', i pop an element from the stack.

my problem is that, no matter what expression i enter, it's always invalid, even if it's just '()' which should be valid.

my code:



any help would be very, Very much appreciated.

and if anyone could also explain to me how to create the stack.c separate from my main function. do i just past them there? or should i put header files?
also, could anyone explain to me what the following warnings mean?
"suspicious pointer conversion"
"non-portable pointer conversion"

When you're including a file that is in the same folder as the source code, you must use quotation marks.

If you used <> then it won't work because the preprocessor only searches through certain directories for the file name. Take your extra functions and stick them in a file called stack.h the use the #include statement in the code block above. That should fix your problem.
Also your pointer warnings mean that you're trying to assign a value to a variable when the variable is not of the same type as the value. For example int a = "hello world" is an example of that. Yours are more subtle because you're assigning char* to chars.

A pointer is a type that holds the memory location of a variable.

back to your code.
In your pop function you have this code:
stack[top] = " ";
now " " is a char*, but stack[top] is a char. If you want to put an empty space in your stack, then do this:
stack[top] = ' ';

At the beginning of your stacktop function you have this code:
stack[top] = data
stack and data are both char arrays, which are used the same way as char*. You're essentially trying to assign a char* to a char.

In your main function you try to assign the memory location of data to ptrdata. Since data is an array, and therefore a pointer all that is necessary for data and ptrdata to reference the same memory is
ptrdata = data
Your while (*ptrdata != NULL) is also erroneous because you're attempting to compare the value referenced by ptrdata and NULL. What you should be trying to do is compare the value of ptrdata and NULL.
while(ptrdata != NULL)

And finally, I think you're trying to test if the stack array is empty. Instead of comparing it to NULL, why don't you just test the value of the top variable? Since it looks like top holds the index of the first element, and when stack is empty top should be -1, just test if top is -1, and then your stack is empty.

I also notice a classic SM* :




i.e. "If (x is not A) or (x is not . Since x cannot be both A and B, the expression is always true.

You want && instead.

Good luck,

Aaron


ps. SM = 'smooth move'; I had a math teacher that used give almost full credit if we got a difficult problem wrong due to a simple mistake. (e.g. he'd mark "-1 SM!" on a twenty point problem)

You could theoretically get an A in the course hardly ever getting any answers right... those were the days...