simple stack

Hi all i am learning C now and i want to make a program that for a simple stack (an integer array) i will insert elements (integers) in the stack until it will be full or remove them until it will be empty.Here is my code:

Code:

---

#define N 2
int stack[N];
int head=0;

#include<stdio.h>
void push(int);
int pop(void);

int main()
{
        int s,k;

        do
        {
                printf("Give your selection\n");
                printf("1.Push\n");
                printf("2.Pop\n");
                printf("3.Finish\n");
                scanf("%d",&s);
                switch(s)
                {
                        case 1:
                        {
                                printf("give an element to push in the stack:\n");
                                r=scanf("%d",&k);
                                if (r==1)
                                        push(k);
                                else
                                {
                                        printf("You don't give a valid number");
                                        return 0;
                                }
                                break;
                        }
                        case 2:
                        {
                                pop();
                                break;
                        }
                }
        }
        while(s!=3);

}

void push(int e)
{
        if (head<N)
                stack[head++]=e;
        else
                printf("STACK IS FULL\n");
}


int pop(void)
{
        if(head>0)
                return stack[--head];
        else
                printf("STACK IS EMPTY\n");
}

---

My problem is that here i declare the array and the index of the stack(head) as global variables but when i try to declare them as local variables in main and pass them to push and pop functions i can't get it to work.Any ideas?

Ok this is probably because you're not passing your variables by reference to you function, and therefore head++ increments the copy of head that you're sending to the function, so head(in main) always stays at 0.

Quote:

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by reference

---

because it is c - not a reference but pointers should be used...

I think the better way is to use a struct

Code:

---

typedef struct
{
  int items[N];
  unsigned int head=0;
}stack;

---

in main declare the variable of this type

stack myStack;

and pass the pointer to it in the push/pop functions

push(&myStack, newValue);

value = pop(&myStack);

Quote:

---

because it is c - not a reference but pointers should be used...

---

Agreed. But from what I remember, sending a variable to a function using a pointer is what's called passing the argument by reference. When you don't use a pointer, it's passing the argument by value.

And I agree that ideally you'd want a structure for the stack, but if the OP wants to stick with his array, those small changes will get him what he desires.