C Program to Implement two Stacks using a Single Array & Check for Overflow & Underflow

#include < stdio.h>
#include < stdlib.h>
#define max 10
 
int top1, top2, array[max];
void push(void)
{
    int x, ch;
    if (top1 == top2 - 1)
    {
        printf("stack overflow \n" );
        return;
    }
    printf("enter a no \n" );
    scanf("%d" , &x);
    printf("\n press 1 to push the element in 1st stack or press 2 for stack 2:" );
    scanf("%d" , &ch);
    if (ch == 1)
        array[++top1] = x;
    else
        array[--top2] = x;
    printf("%d element is successfully pushed \n" , x);
    return;
}
void pop(void)
{
    int y, ch;
    printf("\n press 1 to pop the element from 1st stack or press 2 for from stack 2" );
    scanf("%d" , &ch);
    if (ch == 1)
    {
        if (top1 == -1)    // Condition for checking If Stack 1 is Empty
        {
            printf("stack underflow \n" );
            return;
        }
        y = array[top1];
        array[top1--]=0;
    }
    else
    {
        if (top2 == max) // Condition for checking If Stack 2 is Empty
        {
            printf("stack underflow \n" );
            return;
        }
        y = array[top2];
        array[top2++] = 0;
    }
    printf("%d element is successfully poped from stack \n" , y);
    return;
}
void display(void)
{
    int i;
    if (top1 == -1)
    {
        printf("stack 1 is empty \n" );
    }
    else
    {
        printf("elements of Stack 1 are : \n" );
        for (i = 0; i = top2; i--)
        {
            printf("%d\n" , array[i]);
        }
    return ;
}
 
void main(void)
{
    int ch;
    top1 = -1, top2 = max;
 
    do
    {
        printf("1:push\n 2:pop\n 3:display\n 4:exit\n choice:" );
        scanf("%d" , &ch);
        switch (ch)
        {
        case 1:push();
            break;
        case 2:pop();
            break;
        case 3:display();
            break;
        case 4:printf("quits from program \n" );
            break;
        default:printf("wrong choice \n" );
            break;
        }
    } while (ch != 4);
}

Output

  1 :push
 2 :pop
 3 :display
 4 :exit
choice: 1 
enter a no
 13 
 
press  1  to push the element  in  1st stack or press  2   for  stack  2 : 1 
 13  element is successfully pushed
 1 :push
 2 :pop
 3 :display
 4 :exit
choice: 1 
enter a no
 30 
 
press  1  to push the element  in  1st stack or press  2   for  stack  2 : 1 
 30  element is successfully pushed
 1 :push
 2 :pop
 3 :display
 4 :exit
choice: 1 
enter a no
 37 
 
press  1  to push the element  in  1st stack or press  2   for  stack  2 : 2 
 37  element is successfully pushed
 1 :push
 2 :pop
 3 :display
 4 :exit
choice: 1 
enter a no
 65 
 
press  1  to push the element  in  1st stack or press  2   for  stack  2 : 2 
 65  element is successfully pushed
 1 :push
 2 :pop
 3 :display
 4 :exit
choice: 2 
 
press  1  to pop the element from 1st stack or press  2   for  from stack  21 
30element is successfully poped from stack
 1 :push
 2 :pop
 3 :display
 4 :exit
choice: 2 
 
press  1  to pop the element from 1st stack or press  2   for  from stack  22 
65element is successfully poped from stack
 1 :push
 2 :pop
 3 :display
 4 :exit
choice: 3 
elements of Stack  1  are :
 13 
Elements of stack  2  are
 37 
 1 :push
 2 :pop
 3 :display
 4 :exit
choice: 1 
enter a no
 10 
 
press  1  to push the element  in  1st stack or press  2   for  stack  2 : 1 
 10  element is successfully pushed
 1 :push
 2 :pop
 3 :display
 4 :exit
choice: 1 
enter a no
 98 
 
press  1  to push the element  in  1st stack or press  2   for  stack  2 : 2 
 98  element is successfully pushed
 1 :push
 2 :pop
 3 :display
 4 :exit
choice: 3 
elements of Stack  1  are :
 13 
 10 
Elements of stack  2  are
 37 
 98 
 1 :push
 2 :pop
 3 :display
 4 :exit
choice: 4 
quits from program

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