general palindrome check using stack

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

/**
 * program for general palindrome string
 */

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

#define MAX 100
#define TRUE 1
#define FALSE 0

int push(char *s, int top, char ele)
{

    int i;
    if (top >= MAX)
    {

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

    return top;
}

int pop(char *a, int *top)
{

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

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

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

void main()
{

    int i;
    char a, b;
    char c[MAX];

    int valid = TRUE;
    int TOP = -1;

    char s[MAX];
    printf("Enter string: ");
    gets(c);

    //remember that using gets() function is not safe.
    for (i = 0; i < strlen(c) / 2; i++)
    {

        TOP = push(s, TOP, c[i]);
    }

    for (; c[i] != '\0'; i++)
    {
        if (TOP < 0)
        {

            valid = FALSE;
            break;
        }
        else
        {

            a = pop(s, &TOP);
            if (c[i] != a)
            {

                valid = FALSE;
            }
        }
    }
    if (valid == TRUE)
    {

        printf("Valid palindrome string\n");
    }
    else
    {
        printf("Invalid palindrome string\n");
    }
}