Problem with pushing elements to the stack in c

Question

I implemented a stack in C as follows. And the program is working fine for three pushes but when I try to push more than 3 elements the program executes and the result is printing out but then the error message displays saying that the program has stopped working
My code is as follows :

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

#define MAX 50

//typedef char stackEntryType;
typedef enum{FALSE,TRUE} Boolean;

typedef struct stack{
int top;
int entry[MAX];
}stack;

void createStack(stack *s){
s->top=-1;
}

Boolean IsStackEmpty(const stack *s){
return(s->top==-1);
}

Boolean IsStackFull(const stack *s){
return(s->top==MAX-1);
}

void push(stack *s,int item){
    if(IsStackFull(s)){
        printf("Stack is full\n");
        exit(1);
    }else{
        s->entry[++s->top]=item;
        printf("%d pushed to stack\n",item);
    }
}

void pop(stack *s)
{
    int item;
    if(IsStackEmpty(s))
    {
        printf("Stack is empty\n");
        exit(1);
    }
    else{
        item=s->entry[s->top--];
        printf("%d popped from the stack",item);
    }
}

void main()
{
    stack *s;
    createStack(&s);
    push(&s,1);
    push(&s,2);
    push(&s,3);
    push(&s,4);
    pop(&s);
}

Can someone resolve this issue?

This seems like a good time to learn how to use a *debugger*. First to catch crashes (which is what you have), locate where in your code they happen, and examine the values of all involved variables at the location of the crash. Then you could also use it to step through your code, statement by statement, while monitoring variables and their values to see how they change. — Some programmer dude, Feb 12 '20 at 06:25
A hint though: In the `main` function the type of `&s` is `stack **`. Not really what `createStack` (or `pop`) is expecting, is it? Your compiler should have been able to emit warning about that, so please listen to your compiler. — Some programmer dude, Feb 12 '20 at 06:26
As an extra suggestion what @Someprogrammerdude said, you can use [this](http://pythontutor.com/c.html#mode=edit) really cool tool — sassy_rog, Feb 12 '20 at 06:27

ralf htp · Answer 1 · 2020-02-12T07:07:31.017

Curiously you are smashing your machine's stack with your current code, when compiling it i got :

1 pushed to stack
2 pushed to stack
3 pushed to stack
4 pushed to stack
*** stack smashing detected ***: <unknown> terminated

4386427's answer is right, especially the point with the compiler warnings. Alternatively you can build your stack in the machine's heap (dynamic memory) with malloc() :

struct stack *s = malloc (sizeof (struct stack))

memory allocation in Stack and Heap

If you malloc the memory on the heap you have to change in main() all &s to s :

void main()
{

    struct stack *s = malloc(sizeof(struct stack));
    createStack(s);
    push(s,1);
    push(s,2);
    push(s,3);
    push(s,4);
    pop(s);
    free(s);  // release allocated memory
}

Support Ukraine · Accepted Answer · 2020-02-12T06:50:26.860

There is no stack allocated at all. This

void main()
{
    stack *s;

only gives you a stack-pointer.

Change it to

void main()
{
    stack s;

to get a stack-object.

Notice: Creating the stack as a local variable in main is fine as long as MAX is relative small. If you change MAX to a huge value (e.g. #define MAX 5000000) it is better to allocate memory using malloc. See answer from @ralfhtp.

BTW: Enable compiler warnings. You are passing a stack** to something expecting a stack* The compiler would have warned you and you could have found the bug rigth away.

Problem with pushing elements to the stack in c

2 Answers2