Stack code in C crashes and stops working as soon as it is run

Question

So, I was working on a standard stack program in C with push, pop etc. The code compiles fine but as soon as I run it, it crashes and a 'stopped working' message is shown. I am working on a Dev C++ application on a windows system. The code is given below:

#include <stdio.h>
#include <stdlib.h>

#define MAX 10

struct stack {
    int items[MAX];
    int top;
};
typedef struct stack st;

void createemptyStack(st *s) {
    s->top = -1;
}

int isEmpty(st *s) {
    if (s->top == -1)
        return 1;
    else
        return 0;
}

int isFull(st *s) {
    if (s->top == MAX - 1)
        return 1;
    else
        return 0;
}

int push(st *s) {
    int newitem;

    printf("Enter the value you want to push");
    scanf("%d", &newitem);

    if (isFull(s)) {
        printf("Stack is full");
    } else {
        s->top++;
        s->items[s->top] = newitem;
    }
}

void pop(st *s) {
    if (isEmpty(s)) {
        printf("Stack is empty");
    } else {
        printf("Items popped %d", s->items[s->top]);
        s->top--;   
    }
}

int main() {
    int ch;
    int loop = 1;
    st *s;

    createemptyStack(s);

    do {
        printf("\n ***STACK OPERATIONS");
        printf("\n 1. PUSH");
        printf("\n 2. POP");
        printf("\n 3. EXIT");
        printf("\n ***************");
        printf("\n Enter your choice: ");
        scanf("%d", &ch);

        switch (ch) {
          case 1:
            push(s);
            break;

          case 2:
            pop(s);
            break;

          case 3:
            printf("Visit again");      
            loop = 0;
            exit(0);

          default:
            printf("Invalid choice");
        }   
    } while(loop);

    getch();
}

Would really be helpful for me if you can help me in this matter. I think the problem might reside in the do / while loop but I am not sure. Would like some opinions on this matter.

Answer 1

  st *s;

you are not allocating memory to *s , change it to

  st *s = malloc(sizeof(*s));

or

  st s;
  createemptyStack(&s)

Answer 2

The value of s which is a pointer to st is uninitialized and hence contains garbage data. Now when you pass s to createemptyStack it tries to access memory location pointed by garbage data in s leading to segmentation fault. You first need to allocate space for structure by either defining a struct object

st obj;
st* s = &obj;

or by dynamic memory allocation

s = malloc(sizeof(st))

Answer 3

s is defined as a pointer to a stack object. You need an actual struct stack object for s to point to. Either define one as a local variable:

st obj;
st *s = &obj;

or allocate one from the heap:

st *s = malloc(sizeof(*s));
if (s == NULL) {
    fprintf(stderr, "allocation failure\n");
    exit(1);
}