Implement stack with pointers in c

Question

I try to implement a simple stack in c with pointers and struct but I think I have a problem with push or print. My program prints only the first Node.

If someone could help me to solve this

Here is my code

stack.h

/***********************************************************************
* stack.h
***********************************************************************/

#include <stdbool.h>

#ifndef _STACK_H_
#define _STACK_H_

typedef struct Stack{
    int value;
    struct Stack* next;
}Stack;

Stack initStack();

bool push (Stack* s, int n);

int pop (Stack* s);

bool stackEmpty (Stack s);

void printStack (Stack s);

#endif

stack.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdbool.h>
#include "stack.h"

Stack initStack(){
    Stack s = {0, NULL};
    return s;
}

bool push (Stack* s, int n){
    if (stackEmpty(*s)){
        s->value = n;
        return true;
    }else{
        Stack stack = {n, s};
        s = &stack;
        return true;
    }
    return false;
}

int pop (Stack* s){
    int value = s->value;
    s = s->next;
    return value;
}

bool stackEmpty (Stack s){
    if (s.value == 0 && s.next == NULL)
    return true;
return false;
}

void printStack (Stack s){
    Stack* b = &s;
    printf("Stack : \n");
    while(b != NULL){
        printf("%d\n", b->value);
        b = b->value;
    }

main

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdbool.h>
#include "stack.h"

int main (int argc, char** argv) {

    Stack stack1 = initStack();

    push(&stack1, 5);

    printStack(stack1);
}

S.S. Anne · Accepted Answer · 2020-01-05 23:27:49Z

1

You're taking the address of a local variable here:

Stack stack = {n, s};
s = &stack;

You need to dynamically allocate it:

Stack *stack = malloc(sizeof(*stack));
stack->value = n;
stack->next = s;
s = stack;

For consistency, I would recommend to take and return Stack * instead of Stack, and possibly rename initStack to newStack.

answered Jan 5, 2020 at 23:27

S.S. Anne

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4 Comments

John3136 Over a year ago

I'd use the Stack* as a convention in all the methods - i.e. Pass Stack* params not Stack. Consistency will avoid confusion!

S.S. Anne Over a year ago

@John3136 That's what I'm recommending in the last sentence in my answer (take and return being the most important part).

user11913526 Over a year ago

@JL2210 Thanks its works perfectly ! But I don't understand why I need to use param Stack** on push and i can't use Stack*, I tried also the second case and it didn't worked... I'm a bit confused about that

S.S. Anne Over a year ago

@Marc No, use Stack * for everything. For example, make printStack and stackEmpty take a Stack * and make initStack return a Stack *. Just make sure to dynamically allocate memory (with malloc) in initStack.

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