Stack

#include <stdio.h>

#define MAX 100

typedef struct
{
    int stack[ MAX ];
    int tos;
}stack_t;

void push ( stack_t *p_t, int ele )
{
    if ( p_t->tos   == MAX - 1 )
    {
        printf ( "Stack Overflow.\n" );
        return;
    }
    p_t->stack[ ++p_t->tos ] = ele;
}

int isEmpty ( stack_t t )
{
    return ( t.tos == -1 );
}

int pop ( stack_t *p_t )
{
    if ( isEmpty ( *p_t ) )
    {
        printf ( "Stack Underflow.\n" );
        return -1;
    }
    return p_t->stack[ p_t->tos-- ];
}

int stackTop ( stack_t t )
{
    if ( isEmpty ( t ) )
    {
        printf ( "Stack Empty.\n" );
        return -1;
    }
    return t.stack[ t.tos ];
}

void display ( stack_t t )
{
    int i;
    printf ( "STACK:\t" );
    if ( isEmpty ( t ) )
    {
        printf ( "Stack Empty.\n" );
        return;
    }
    for ( i = t.tos; i > -1; i-- )
        printf ( "%6d\t", t.stack[ i ] );
    printf ( "\n" );
}

void main ( )
{
    stack_t s;
    int choice, ele;
    s.tos = -1;
    while ( 1 )
    {
        printf ( "1:\tPush\n2:\tPop\n3:\tStack Top\n4:\tDisplay\n0:\tEXIT\nCHOICE:\t" );
        scanf ( "%d", &choice );
        printf ( "\n" );
        if ( !choice )
            break;
        switch ( choice )
        {
        case 1:
            printf ( "Enter element to push:\t" );
            scanf ( "%d", &ele );
            push ( &s, ele );
            display ( s );
            break;
        case 2:
            if ( isEmpty ( s ) )
            {
                printf ( "Stack Underflow.\n" );
                continue;
            }
            printf ( "Popped element:\t%d\n", pop ( &s ) );
            display ( s );
            break;
        case 3:
            if ( isEmpty ( s ) )
            {
                printf ( "Stack Empty.\n" );
                continue;
            }
            printf ( "Stack Top:\t%d\n", stackTop ( s ) );
            break;
        case 4:
            display ( s );
            break;
        default:
            printf ( "Invalid Input.\nTry Again.\n" );
            continue;
        }
    }
    display ( s );
}