factorial using stack

/****************************
 *  Umang B Bhatt            *
 *   bhatt.umang7@gmail.com  *
 *****************************/

/**
 * program for factorial using stack
 */

#include<stdio.h>
#include<string.h>

#define MAX 100

// push method
int push(int *s, int top, int ele)
{

    int i;
    if (top >= MAX)
    {

        printf("\nStack Overflow");
    }
    else
    {
        s[++top] = ele;
    }

    return top;
}


//pop method
int pop(int *a, int *top)
{

    if ((*top) >= 0)
    {
        (*top) = (*top) - 1;

        return a[(*top) + 1];
    }
    else
    {

        printf("Stack underflow\n");
        return 0;
    }
}


// personally, i believe that declaring TOP and S here is bad practice


void main()
{
    int n;

    int i; // loop variable


    int ans = 1 ; // stroes the final answer

    int TOP = -1; // stack variables that mainntain stack's top


    int s[MAX]; // the stack


    printf("\nEnter number: ");

    scanf("%d",&n);


    // here we can also make sure that the use is not entering a number 
    // that can not be accomodated in the stack

    // if the user enters a number less than or equal to 0
    // then we can not find factorial
    if(n<=0)
    {

        printf("\nThe number can not be less than 0");
    }
    else
    {
        // push the numbers n,n-1 ....1 in the stack
        // you can also go in reverse manner here. the result will be the same
        // because in multiplication, order does not matter
        for(i = n ; i >0 ; i--)
        {

            TOP = push(s,TOP, i);
        }

        // now pop all the elements one by one
        // multiply them with the answer variable

        while(TOP>=0)
        {
            ans = ans * pop(s,&TOP);
        }

  
        printf("\nFactorail is %d\n",ans);
  
    }

    // getch();  // will not work on linux
}