User-defined Manipulators

// User-defined manipulators
#include <iostream>
std :: ostream& tab ( std :: ostream& o ) 
{
	return o << "\t" ;
}
class roman
{
	private :
		
		std :: string str ;
	public :
		
		roman ( std :: string s ) 
		{
			str = s ;
		}
		friend std :: ostream& operator << ( std :: ostream&, const roman& ) ;
} ;
std :: ostream& operator << ( std :: ostream& o, const roman& r ) 
{
	struct key
	{
		char ch ;
		int val ;
	} ;
	key z[ ] = {
					{'m', 1000}, 
					{'d', 500}, 
					{'c', 100}, 
					{'l', 50}, 
					{'x', 10}, 
					{'v', 5}, 
					{'i', 1}
			   } ; 
	int num = 0 ;
	int prev ;
	int sz = sizeof ( z ) / sizeof ( z[ 0 ] ) ;
	
	for ( int i = 0 ; i < r.str.length ( ) ; i++ ) 
	{
		int j ;
		
		for ( j = 0 ; j < sz ; j++ ) 
		{
			if ( z[ j ].ch == r.str[ i ] ) 
			{
				break ;
			}
		}
		
		num = num + z[ j ].val ;
		if ( i != 0 && prev < z[ j ].val ) 
			num = num - 2 * prev ;
		prev = z[ j ].val ;
	}
	
	o << num ;
	
	return o ;			
}
int main( ) 
{
	std :: string str1 = "viii" ;
	std :: string str2 = "mcmxcviii" ;
	std :: cout << "Roman: " << str1 << tab << "Dec: " << roman ( str1 ) << std :: endl;
	std :: cout << "Roman: " << str2 << tab << "Dec: " << roman ( str2 ) << std :: endl;
	return 0 ;
}