function isLetter (c)
{   return ( ((c >= "a") && (c <= "z")) || ((c >= "A") && (c <= "Z")) )
}

function isDigit (c)
{   return ((c >= "0") && (c <= "9"))
}
		
function isLetterOrDigit (c)
{   return (isLetter(c) || isDigit(c))
}		

function isInteger (s)		
{   var i;

    if (isEmpty(s)) 
       if (isInteger.arguments.length == 1) return defaultEmptyOK;
       else return (isInteger.arguments[1] == true);

    // Search through string's characters one by one
    // until we find a non-numeric character.
    // When we do, return false; if we don't, return true.

    for (i = 0; i < s.length; i++)
    {   
        // Check that current character is number.
        var c = s.charAt(i);

        if (!isDigit(c)) return false;
    }

    // All characters are numbers.
    return true;
}

function isDate (year, month, day) {
	// month argument must be in the range 1 - 12
	month = month - 1; // javascript month range : 0- 11
	var tempDate = new Date(year,month,day);
	
	if ( (year == tempDate.getFullYear()) &&
		(month == tempDate.getMonth()) &&
		(day == tempDate.getDate()) )
		return true;
	else
		return false
}

function isValidEmail(str) {
   return (str.indexOf(".") > 0) && (str.indexOf("@") > 0); 
}

function IsNumeric(strString) {
   var strValidChars = "0123456789.-";
   var strChar;
   var blnResult = true;

   if (strString.length == 0) return false;

   //  test strString consists of valid characters listed above
   for (i = 0; i < strString.length && blnResult == true; i++)
      {
      strChar = strString.charAt(i);
      if (strValidChars.indexOf(strChar) == -1)
         {
         blnResult = false;
         }
      }
   return blnResult;
}

function check_required_email (field, message) {	
	if ( ! check_field(field, message) ) return false;
	
	if (! isValidEmail(field.value)) {
		alert(message);
		field.focus();
		return false;
	}
	else 
	 	return true;
}

function check_required_number (field, message) {	
	if ( ! check_field(field, message) ) return false;
	
	if (! IsNumeric(field.value)) {
		alert(message);
		field.focus();
		return false;
	}
	else 
	 	return true;
}


function check_date(field, message) {

	if ( check_field(field, message) ) {
		var myDate = field.value;
		
		var myDate=field.value.split("/");
		day = myDate[0];
		month = myDate[1];
		year = myDate[2];
	
		if (isDate(year, month, day)) {
			return true;	
		}
		else {
			alert(message);
			return false;	
		}	
	}
	else 
		return false;	
	
}

function check_required_field(field, message) {
	if (field.value == "") {
		alert(message);
		field.focus();
		return false;
	}
	else 
	 	return true;
}

function check_password (passwd_field, passwd2_field, message1, message2) {
	
	if (passwd_field.value == passwd_field.value) {
		if (passwd_field.value.length >= 6 ) {
			return true;
		} else {
			alert(message1);
			passwd_field.focus();
			return false;				
		}	
	} else {
		alert(message2);
		passwd_field.focus();
		return false;		
	}
}

// minstens één checkbox
function check_checkbox(field, message) {
	for (i=0;i<field.length;i++)	{
		if (field[i].checked) {
			return true;
		}
	}		
	alert(message)
	return false;		
}

// een radio button
function check_radio(field, message) {
	for (j=0; j < field.length; j++)	{
		if (field[j].checked) {
			return true;		
		}			
	}		
	alert(message)
	return false;			
}

// een selection list 
function check_selection (field, message) {
	// -kies-
	if ( field.options.selectedIndex > 1)
		return true;
			
	alert(message)
	return false;			
}


function selectAll (list) {
	for (i=0; i< list.length; i++) {
		list.options[i].selected = true; 	
	}	
}