Thread: Making a Stack using Pointers

Hi remember me? I posted here a few months ago with a problem using a stack. Well now I’m using the same stack code again but trying to make the stack with pointers (yay I’m learning pointers!). Anyway I have been playing with this code for a long time and I am nearly insane because it is not working and I cant find out where the problem is. I know it is probably a stupid and small mistake of mine but I cant find it.
When this program is run if the input is 123 the output should be 321
I’m sure that this code is very easy to understand for anyone who knows C better than me so please tell me what is wrong with my code before I go crazy.
Thankyou.

Code:

#include <stdio.h>
#include <stdlib.h>
#define STACK_SIZE 50
#define TRUE 1
#define FALSE 0

typedef int Bool;

void make_empty(void);
Bool is_empty(void);
Bool is_full(void);
void push(int i);
int pop(void);
void stack_overflow(void);
void stack_underflow(void);

int contents[STACK_SIZE];
int *top_ptr = &contents[0];

int main()
{
  int temp = 0;

  make_empty();
  printf("Enter some digits: ");
  while ((temp = getchar()) != '\n') {
    push(temp);
  }

  printf("Contents of stack (should be reversed): ");
  while (!is_empty()) {
    printf("%d", pop());
  }
  printf("\n");

  return 0;
}

void make_empty(void)
{
    top_ptr = &contents[0];
}

Bool is_empty(void)
{
    return top_ptr == &contents[0];
}

Bool is_full(void)
{
    return top_ptr == &contents[STACK_SIZE];
}

void push(int i)
{
    if (is_full())
        stack_overflow();
    else
        *top_ptr++ = i;
}

int pop(void)
{
    if (!is_empty())
    return *--top_ptr;
    else
        stack_underflow();

    return 0;
}

void stack_overflow(void)
{
  printf("Stack Overflow!\n");
  exit(EXIT_FAILURE);
}

void stack_underflow(void)
{
  printf("Stack Underflow!\n");
  exit(EXIT_FAILURE);
}

I don't understand.
If getchar returns an int, and I want it to be an int, and the person inters an int then why do I need to check if it is an int and convert it to an int?

Can you please show me exactly how to do it?

I have been looking at this code for so long and I just cant find the problem

One reason I don't understand why I need to check if it is an int is because I have done similar programs before and it works like this..... I am sure i'm missing something so please show me what it is as I have gone a complete blank

Thankyou

So I need to right isdigit()?
I hope I get this done ok... i'll see what I can do and post what happens.
Thankyou

Thankyou I finally made it work

I have just a few more questions.

Does this mean getchar() returns a char and I am "converting it" to an int? (It's called getchar so I guess thats what it does...)

And, what "exactly" does the line
temp = temp - '0';
Do?

Is this the prefered way to do it or is there a better way?

Thanks, I think I understand that ok...

>It is the easiest way for single digit numbers.
What about larger numbers? What's another way to do it?