function ccValidate(f) 
  {   // Validates the credit card form used in classCredit
    var errMessage="";
	var errFound=false;

    if (f.forename.value=="" || f.surname.value=="" || isblank(f.forename.value) || isblank(f.surname.value)) 
	{
      errMessage+="Please enter your Name\n";
	  if (!errFound) {f.forename.focus(); errFound=true;}
    }

    e=f.cardNumber;
    if (e.value=="" || e.value==null || isblank(e.value)) 
	{
      errMessage+="Please enter your Card number\n";
	  if (!errFound) {f.cardNumber.focus(); errFound=true;}
    }
	
    else {
	  var opt=f.cardType.selectedIndex; // Get index of selected option
	  var ccType=f.cardType[opt].text;  // Retrieve displayed text of selected option
	  var z=IsCCNumberValid(e.value, ccType);

      if (z==0) 
	  {
	    errMessage+="The Card number is invalid for that type\n";
    	if (!errFound) {f.cardNumber.select(); errFound=true;}
	  } 
	  
    }
	
	if (f.cardEndYear.value<f.cardStartYear.value ||(f.cardEndYear.value==f.cardStartYear.value && f.cardEndMonth.value<=f.cardStartMonth.value))
	{
	  errMessage+="Card End date must be later than card Start date\n";
	  if (!errFound) {f.cardEndMonth.focus(); errFound=true;}
	}
	
    if (errMessage!="") 
	{
     alert (errMessage);
     return false;
    }
	else return true;
  }

  function IsCCNumberValid(ccNumber, cardType)
  { // Validates a credit card number for Mastercard, Visa, Amex & Diners Club
	ccNumber=ccNumber.replace(/ /g,"");  // Remove any blanks before validating
    if (ccNumber=="M1111") {return 1;}  // Value for testing
    var retval=0;
    if(cardType!=null)
    {
	   if(cardType == "Mastercard"){retval = isMCRD(ccNumber);}
       else if(cardType == "Visa"){retval = isVISA(ccNumber);}
       else if(cardType == "American Express"){retval = isAMEX(ccNumber);}
       else if(cardType == "Diners Club"){retval = isDCCB(ccNumber);}
	   else {retval=modTen(ccNumber);}
    }
    else
    {
       if(!retval){retval = isMCRD(ccNumber);}
       if(!retval){retval = isVISA(ccNumber);}
       if(!retval){retval = isAMEX(ccNumber);}
       if(!retval){retval = isDCCB(ccNumber);}
	   if(!retval)  {retval=modTen(ccNumber);}
    }
    return retval;
  }

  function isMCRD(ccNum)
  { // Validates a Mastercard number
    var preFix = ccNum.substr( 0, 2);
    if(preFix == "51" || 
       preFix == "52" || 
       preFix == "53" || 
       preFix == "54" || 
       preFix == "55")
    {	
       if(ccNum.length == 16){return  modTen(ccNum);}
    }
    else
    {
      return 0;
    }
  }
  
  function isVISA(ccNum)
  { // Validates a Visa number
	var preFix = ccNum.substr(0, 1);
    if(preFix == "4"){	
       if(ccNum.length == 13 || ccNum.length == 16){return  modTen(ccNum);}
	}
    else
    {
       return 0;
    }
  }

  function isAMEX(ccNum)
  { // Validates an Amex number
    var preFix = ccNum.substr(0, 2);
    if(preFix == "34" || preFix == "37"){	
       if(ccNum.length == 15){return  modTen(ccNum);}
	   else {return 0;}
	}
    else
    {
       return 0;
    }
  }

  function isDCCB(ccNum)
  { // Validates a Diners Club number
	preFix = ccNum.substr(0, 3);
    if(preFix == "300" || 
       preFix == "301" || 
       preFix == "302" || 
       preFix == "303" || 
       preFix == "304" || 
       preFix == "305")
    {	
       if(ccNum.length == 14){return  modTen(ccNum);}
       else {return 0;}
    }
	preFix = ccNum.substr(0, 2);
    if(preFix == "36" || preFix == "38"){	
       if(ccNum.length == 14){
	   return  modTen(ccNum);
	   }
	   else {return 0;}
	}
    else
    {
       return 0;
    }
  }
 
  
  function modTen(ccNum)
  { // Modulus 10 calculator used by all credit cards
	var numLen = ccNum.length;
    var tot=0;
    for(var x = numLen; x > 0; x-=2){
	  var a=ccNum.substr(x - 1, 1)-0;  // Extract alternate digits as numbers
	  tot=tot+a; // and add to the checksum
	}
    for(x = numLen - 1; x > 0; x-=2)
    {
       var y = (ccNum.substr(x - 1, 1)-0) * 2;  // Extract the other alternate digits as numbers, double
	                                            // and add each digit of the result to the checksum
       var z=y+"";
       if(z.length == '1'){tot+=y;}
       if(z.length == '2'){tot=tot+1; tot=tot+y-10; }
    }
	tot=tot+"";
    if(tot.substr(tot.length - 1, 1) == '0'){return 1;}
    else{return 0;}
  }
  
  function checkIfFull(fieldNo)
  { // Used with classCreditCard to move cursor to next part of card number entry
    // when 4 digits entered in current one
    var eName="cardNumber" + fieldNo;
	var e=getElement(eName);
	if (e.value.length<4) {return;}
	var nextField=Number(fieldNo) + 1;
	var nextName="cardNumber" + nextField;
	e=getElement(nextName);
	e.focus();
  }



  function checkDate(d,m,y)
  { // Checks for valid date in range 1/1/1900 to 31/12/2099
    if (!isNumeric(d) || !isNumeric(m) || !isNumeric(y)) {return false;}
	if (m<1 || m>12) {return false;}
	if (y<1900 || y>2099) {return false;}
    var daysInMonth=new Array(31,28,31,30,31,30,31,31,30,31,30,31);
	if (y%1000==0 ||(y%4==0 && y%100!=0)) {daysInMonth[1]=29;}
	if (d<1 || d>daysInMonth[m-1]) {return false;}
	return true;
  }
  

  function checkEmail(email)
  { // this checks for a valid format email address
    var pattern=/^[a-zA-Z0-9]+([.|_|-][a-zA-Z0-9]+)?[@]{1}[a-zA-Z0-9]+([.|_|-][a-zA-Z0-9]+)*[.]{1}[a-zA-Z0-9]{2,3}$/;
    var result=email.match(pattern);
    if (result==null)
      {
       return false;
      } 
      else  return true;
  }


  function checkForm(f)
  {
//  alert ("Here in checkForm");
//  alert ("Name=" + f.name);

/*   To test the chosen option in a Select statement:
	      var opt=f.selectname.selectedIndex;
		  var field=f.selectname.options[opt].text; 

 (Can use value instead of text if the option statements have a value clause)
*/
	if (f.buttonPressed.value=="Cancel") {return true;}
    if (f.buttonPressed.value=="Delete") 
	{
	  if (confirm("Are you really sure you want to delete this record?"))
	  {return true;}
	  else {return false;}
	}
    var errMsg="";
	
	switch (f.name)
	{
	  case "contactForm":
        if (empty(f.contactName.value)) 
	    {
	      if (errMsg=="") {f.contactName.focus();}
          errMsg+="Please enter your Name\n";
        }
  
  
        if (empty(f.phone.value) && empty(f.email.value)) 
        {
	      if (errMsg=="") {f.phone.focus();}
          errMsg+="Please enter either your Telephone Number or Email Address\n";
        }

        if (!empty(f.email.value) && !checkEmail(f.email.value)) 
        {
	      if (errMsg=="") {f.email.focus();}
          errMsg+="That Email address is invalid\n";
        }
	
 	
      break;
	  
	  
	  default:
	    return true;
	}

	if (errMsg!="")
	{
	  alert(errMsg);
	  return false;
	}
	else return true;
  }

  
  function checkPass(pass)
  { // This checks password is 6-12 chars, starts with a letter and contains 
    // only alphanumerics
    
	if (pass.length<6 || pass.length>12) {return false;}
	var pattern=/^[a-zA-Z][a-zA-Z0-9]{0,11}$/;
    var result=pass.match(pattern);
    if (result==null)
      {
       return false;
      } 
      else  return true;
  }

  function checkPhoneNo(phone)
  { // This checks a phone number contains at least 11 digits. It
    // ignores blanks and hyphens
	var p=phone.replace(/ |-/g,""); // Remove blanks or hyphens
	if (p.length<11 || !isNumeric(p)) {return false;}
	else {return true;}
  }
   
  function checkTime(h,m)
  {
    if (!isNumeric(h) || !isNumeric(m)) {return false;}
	if (h<0 || h>23) {return false;}
	if (m<0 || m>59) {return false;}
	return true;
  }

  function checkURL(URL)
  { // this checks for a valid format URL 
    // NB this does not check anything beyond the basic address - ie no parameters 
	var patternFormat=/^(http\:\/\/)?(www\.)?[a-zA-Z0-9]+([.|_|-][a-zA-Z0-9]+)+[.]{1}[a-zA-Z0-9]{2,3}/;
    var result=URL.match(patternFormat);
    if (result==null)
      {
       return false;
      } 
      else  return true;
  }
  
  function empty(s)
  {
    if (s=="" || s==null || isblank(s)) {return true;}
	else {return false;}
  }
	
  function generateRandomNo(x, y) 
  { // This function generates a random integer between x & y
    var range = y - x + 1;
    return Math.floor(Math.random() * range) + x;
  }
  
  function getElement(id)
  {
    if (document.getElementById) {var elmt=document.getElementById(id);}
    else
    {
      if (document.all) {var elmt=document.all[id];}
	  else
	  {
	    if (document.layers) {var elmt=document.layers[id];}
	    else elmt=false;
	  }
    }
    return elmt;
  }

  function isblank (s) 
  { // Returns false if field contains any non-blank chars other than new line
    for (var i=0; i<s.length; i++) {
      var c=s.charAt(i);
	  if (c!=" " && c!="\n" && c!="") {
	  return false;
	  }
    }
    return true;
  }


  function isNumeric (number, decPlaces)
  { // This function checks for numerics with a maximum of decPlaces decimal places
    var pattern=/^[0-9]+$/;
    if (decPlaces!=undefined && decPlaces!='0')
	{ // Decimal places allowed
	  var dPlaces=2;
	  var strPlaces=String(decPlaces);
      var result=strPlaces.match(pattern);
	  if (result)  {dPlaces=decPlaces;}
	  pattern=eval("/^[0-9]+([.][0-9]{1," + dPlaces + "})?$/");
    }
	var result=number.match(pattern);
	return result;
  }
  
  
  function newWindow(url, w, h)
  { // Opens URL w in a new window positioned top left and ensures it has the focus
    if (!w) {var wide=400;} else {wide=w;}
	if (!h) {var high=450;} else {high=h;}
	var paras="width=" + wide + ",height=" + high + "align=center scrollbars=yes, left=0, top=0, screenx=0, screeny=0";
    var x=window.open(url, "newWindow", paras);
	x.window.focus();
  }
  
  function validateSlashDate(ddmmyy)
  {
    var dateArray=ddmmyy.split("/");
	var d=dateArray[0];
	var m=dateArray[1];
	var y=dateArray[2];
	if (empty(d) || empty(m) || empty(y)) {return false;}
	var valid=checkDate(d, m, y);
	return valid;
  }

  function formatEmail(name, site, suffix, text, paras, className)
  {
     // <SCRIPT language="Javascript">formatEmail("name", "site", "suffix", "text", "paras", "class");</SCRIPT>
     if (empty(suffix)) {suffix="co.uk";}

     var emailAddress=name + "@" + site + "." + suffix;
     document.write ("<a href='mailto:" + emailAddress);
     if (!empty(paras)) {document.write ("?" + paras);}
     document.write ("'");
     if (!empty(className)) {document.write (" class='" + className + "'");}
     document.write (">");
     if (empty(text)) {document.write (emailAddress);} else {document.write (text);}
     document.write ("</a>\n");
  }