function checkMail(){

  data = new Array(6);
  var text = "";

  var allOk = true;
  var cardSelected = true;

  if (document.forms[0].elements[0].value.length < 2){
    allOk = false;
    data[0] = "Name"; 
  }
  
  if (document.forms[0].elements[1].value.length < 3){
    allOk = false;
    data[1] = "Surname";
  }

  if (document.forms[0].elements[11].value < 1){
    allOk = false;
    data[2] = "Amount";
  }

  if (document.forms[0].elements[12].value == "Check"){
    cardSelected = false;
  }
  
  if (cardSelected){
    if (document.forms[0].elements[13].value.length < 16){  
      allOk = false;
      data[3] = "Card number (16 digits)"; 
    }

    if (document.forms[0].elements[14].value.length < 1){  
      allOk = false;
      data[4] = "Expiry Month"; 
    }

    if (document.forms[0].elements[15].value.length < 1){  
      allOk = false;
      data[5] = "Expiry Year"; 
    }
    
  }
  

  if (allOk){
    return true;
  }
  else{
    text += "Please complete the following fields:\n\n";
    
    for (i=0; i < 6; i++){
     if (data[i]){
       text += "* ";
       text += data[i];
       text += "\n";
     }
    }

    alert(text);
    return false;
  }

}