C Program for Program to calculate prime number

/* Program to calculate prime number */
main( )
{
int   num, i ;
printf ( "Enter a number " ) ;
scanf ( "%d", &num ) ;
i = 2 ;
while ( i <= num - 1 )
{
if ( num % i == 0 )
{
printf ( "Not a prime number" ) ;
break ;
}
i++ ;
}
if ( i == num )
printf ( "Prime number" ) ;
}