TWO STACKS IN ONE ARRAY IN C CODE

#include<stdio.h>
#define MAX 10
int top1 = -1;
int top2 = MAX;
int a[MAX];
void push(int e,int s);
int pop(int s);

int main()
{
    int n ,e,s;
    do
    {
        printf("\n enter choice \n 1 for push \n 2 for pop \n 3 for exit \n  ");
        scanf("%d",&n);
        switch(n)
        {
            case 1:
            {
                printf("\n choose the stack 1 or 2 \n");
                scanf("%d",&s);
                printf("\n enter the element \n");
                scanf("%d",&e);
                push(e,s);
                break;
            }
            case 2:
            {
             int e;
             printf("\n enter your stack preffrence 1 or 2 ");
             scanf("%d",&s);
             e = pop(s);
             if(e != -1)
             {
                 printf("\n the pop element = %d \n",e);
             }
             break;
            }
            default:
            printf("\n enter the correct choice \n");
        }
    }while(n!=3);
}
int pop(int s)
{
    int temp;
    if(s==1)
    {
        if(top1==-1)
        {
            printf("stack 1 is empty \n");
            return -1;
        }
        else
        {
            temp = a[top1];
            top1--;
           return temp;
        }
   }
else
{
    if(top1==MAX)
        {
            printf("stack 2 is empty \n");
            return -1;
        }
        else
        {
            temp = a[top2];
            top2++;
           return temp;
        }
}
}
void push(int e,int s)
{
    if(top1==top2)
        {
            printf("\n the queue is full");
            return;
        }
    else
  {
    if(s==1)
    {
        top1++;
        a[top1]=e;
        printf("\n element inserted in stack 1 \n");
    }
  else
 {
     top2--;
     a[top2]==e;
     printf("\n element inserted into stack 2 \n ");

  }
    }

}