#include <stdio.h>
#include <stdlib.h>

int fact( int num );

main()
{
     int num;

     printf( "\nPlease enter a number:  " );
     scanf( "%d", &num );

     if ( num < 0 )      /* legal input? */
        printf( "\nERROR -- number must be >= 0.\n" );
     else
        printf( "\nFactorial of %d is %d.\n", num, fact( num ) );

     return EXIT_SUCCESS;
}

int fact( int num )
{
     if ( num <= 1 )         /* base cases */
        return 1;
     else                    /* recursive call */
        return num * fact( num - 1 );
}