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 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 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 allow 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 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");
  }


 function getElement(id)
 {
   if (document.getElementById)
   {
     var elmt=document.getElementById(id);
   }
   else
   {
     if (document.all)
         {
           var elmt=document.all[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(w)
  { // Opens URL w in a new window positioned top left and ensures it has the focus
    var x=window.open(w,"newWindow", "width=600, height=650, align=center scrollbars=yes, left=0, top=0, screenx=0, screeny=0");
        x.window.focus();
  }

  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 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;
  }