Thread: trying to fix this code...

I'm working on postfix notation calculator. Using stacks (array implementation. I used code from my textbook, apart from functions, I'm allowed to do this. However, It does not work. After fixing lots of mistakes (from the code from the textbook), I get the following result:

Enter the postfix string: 4 5 +
5
Value of the expression is: 0.

I have 3 hours left to finish this, please help me.
The code is in the file.
Thanks for taking a look at this.

You're very close and your code style is excellent. I didn't immediately spot the error but my compiler did:

Code:

stack.c(43) : warning C4700: local variable 'c' used without having been initialized

Also, remember that atoi expects a nul terminated string.

So in summary, you need to change the highlighted section of the code:

Code:

   for(i = 0; i < howlong; i++)
   {  
      s[0] = c;
      
      PostfixString[i] = c;
      
      if(isdigit(c))
      {

You should also read this faq entry.

I did read, unfortunately it is a little above the level of my C knowledge...
I also made some changes, and now the stack is empty and I cannot retrieve the result.
The changes were made in the following part of code:

Code:

 int LeftOperand, RightOperand, Result;
   int i;
   char c;
   char *s = "";  
  /* int howlong; */
   Stack EvalStack; 
   char *PostfixString;


   initialize(&EvalStack);

   printf("Enter the postfix string: ");
   gets(PostfixString); 
   
   /* howlong = strlen(PostfixString);
   printf("%d \n", howlong);  */

   for(i = 0; PostfixString[i] != '\0'; i++)
   {

That section of code was fine except for the use of gets instead of fgets. The changes required have been highlighted:

Code:

   printf("Enter the postfix string: ");
   fgets(PostfixString, sizeof(PostfixString), stdin); /* gets is bad. */
   
   howlong = strlen(PostfixString);
   printf("%d \n", howlong);

   for(i = 0; i < howlong; i++)
   {  
      c = PostfixString[i]; /* Get a character, this was the wrong way around. */

      s[0] = c;
      s[1] = '\0'; /* Make sure the number string is nul terminated. */
      
      if(isdigit(c))
      {

Thank you, thank you! We did not go through the fgets, fscanf etc functions yet, but I do not think it will be a problem. Can't wait for summer to have more time to study...
Thanks again.