function isValidInteger( value ) {
	var chr;
	for ( var i = 0;  i < value.length;  i++ ) {
		chr = value.charAt( i );
		if ( chr > '9' || chr < '0' )
			{ 
				return false; 
			}
	}
	return true;
}

function isValidPrice( value ) {
	var chr;
	for ( var i = 0;  i < value.length;  i++ ) {
		chr = value.charAt( i );
		if ( chr > '9' || chr < '0' ) {
			if ( chr != ',' && chr != '.' ) 
				{ 
					return false; 
				}
		}
	}
	return true;
}

function isValidWeight( value ) {
	var chr;
	for ( var i = 0;  i < value.length;  i++ ) {
		chr = value.charAt( i );
		if ( chr > '9' || chr < '0' ) {
			if ( chr != ',' && chr != '.' ) 
				{ 
					return false; 
				}
		}
	}
	return true;
}

function CheckQty(form) { 

	if (form.q.value == "" ) { 
		alert ( "Please enter quantity of books to purchase" );  
		form.q.value=1; 
		form.q.focus(); 
		return false; 
	} ;

	if ( ! isValidInteger(form.q.value) ) { 
		alert ( "The quantity you choose must be a number" ); 
		form.q.value=1; 
		form.q.focus(); 
		return false; 
	}

	return true;

}

function CheckAddress(form) { 

	if (form.orderName.value == "" ) { 
		alert ( "Please enter your name" );  
		form.orderName.focus(); 
		return false; 
	} ;

	if (form.orderAddress.value == "" ) { 
		alert ( "Please enter your delivery address" );  
		form.orderAddress.focus(); 
		return false; 
	}

	if (form.orderCity.value == "" ) { 
		alert ( "Please enter your City" );  
		form.orderCity.focus(); 
		return false; 
	} ;

	return true;

}


function CheckPayment(form) { 

	var cardSelected = false;

	for (i=0; i<form.orderCard_type.length; i++) 
		{
			if (form.orderCard_type[i].checked) 
				{
					cardSelected = true;
				}
		}

	if ( !cardSelected ) { 
		alert ( "Please select the type of credit card you have" );  
		return false; 
	} ;

	if (form.orderCard_name.value == "" ) { 
		alert ( "Please enter the name shown on your credit card" );  
		form.orderCard_name.focus(); 
		return false; 
	} ;

	if (form.orderCard_number.value == "" ) { 
		alert ( "Please enter the number of your credit card" );  
		form.orderCard_number.focus(); 
		return false; 
	} ;

	return true;

}

function CheckBook(form) { 

	if (form.title.value == "" ) { 
		alert ( "Please enter a title for the book" );  
		form.title.focus(); 
		return false; 
	} ;

	if ( ! isValidPrice(form.price.value) ) { 
		alert ( "Price must be a number" );  
		form.price.focus(); 
		return false; 
	}

	if ( ! isValidWeight(form.weight.value) ) { 
		alert ( "Weight must be a number" );  
		form.weight.focus(); 
		return false; 
	}

	return true;

}