Implements array as a stack.

C: Program implements array as a stack.

#include <stdio.h>
#include <conio.h>

#define MAX 10

struct stack
{
    int arr[MAX] ;
    int top ;
} ;

void initstack ( struct stack * ) ;
void push ( struct stack *, int item ) ;
int pop ( struct stack * ) ;

void main( )
{
    struct stack s ;
    int i ;

    clrscr( ) ;

    initstack ( &s ) ;

    push ( &s, 11 ) ;
    push ( &s, 23 ) ;
    push ( &s, -8 ) ;
    push ( &s, 16 ) ;
    push ( &s, 27 ) ;
    push ( &s, 14 ) ;
    push ( &s, 20 ) ;
    push ( &s, 39 ) ;
    push ( &s, 2 ) ;
    push ( &s, 15 ) ;
    push ( &s, 7 ) ;

    i = pop ( &s ) ;
    printf ( "\n\nItem popped: %d", i ) ;

    i = pop ( &s ) ;
    printf ( "\nItem popped: %d", i ) ;

    i = pop ( &s ) ;
    printf ( "\nItem popped: %d", i ) ;

    i = pop ( &s ) ;
    printf ( "\nItem popped: %d", i ) ;

    i = pop ( &s ) ;
    printf ( "\nItem popped: %d", i ) ;

    getch( ) ;
}

/* intializes the stack */
void initstack ( struct stack *s )
{
    s -> top = -1 ;
}

/* adds an element to the stack */
void push ( struct stack *s, int item )
{
    if ( s -> top == MAX - 1 )
    {
        printf ( "\nStack is full." ) ;
        return ;
    }
    s -> top++ ;
    s -> arr[s ->top] = item ;
}

/* removes an element from the stack */
int pop ( struct stack *s )
{
    int data ;
    if ( s -> top == -1 )
    {
        printf ( "\nStack is empty." ) ;
        return NULL ;
    }
    data = s -> arr[s -> top] ;
    s -> top-- ;
    return data ;
}