Solution Review: Compare Two Given Dates

# include <stdio.h>

struct date
{
	int day, month, year ;
} ;

int checkDate ( struct date *dt );
int compareDates ( struct date d1, struct date d2 ); 


int main( )
{
int flag1, flag2, flag3 ;
	struct date d1 = {21, 3, 2019};
	struct date d2 = {21, 3, 2019};
	
	flag1 = checkDate ( &d1 ) ;
	flag2 = checkDate( &d2 ) ;
	
	if ( flag1 == 1 || flag2 == 1 )
		printf ( "Invalid date\n" ) ;

	int flag ;
	flag = compareDates( d1, d2 ) ;
	printf ( "flag = %d", flag ) ;
	
	return 0 ;
}
// Check if the format of date is valid or not
int checkDate ( struct date *dt )
{
	// Check if date is invalid
	if ( ( dt -> day > 31 || dt -> day < 0 ) || 
		( dt -> month > 12 || dt -> month < 0 ) || 
		( dt -> year > 9999 || dt -> year < 1000 ) )
		// If date is invalid return -1
		return ( -1 ) ;
	else
	    // If date is valid return 0
		return ( 0 ) ;
}

// Check if the dates are equal or not
int compareDates ( struct date d1, struct date d2 ) 
{
	// Declare varaibles of type int
	int flag1, flag2;
    // Check if the d1 is in valid format
	flag1 = checkDate ( &d1 ) ;
	 // Check if the d2 is in valid format
	flag2 = checkDate( &d2 ) ;
    // If one of the date is invalid then return -1
	if ( flag1 == -1 || flag2 == -1 ){
		return -1;
	}
    // Check if dates are equal
	if ( ( d1.day == d2.day ) && ( d1.month == d2.month ) && 
    ( d1.year == d2.year ) )
	    // If dates are equal then return 0
		return 0 ; 
	else
	    // If dates are not equal then return 1
		return 1 ;
}