Test to see if text in text box starts with a C

Bob,

   I added this javascript to my page, but this only stops the page from adding if the Validation Qty. box is not filled in at all. It does not worry if the part number box starts with a C or not. How do I do a wildcard in Javascript that says if the Part number starts with a C, then only require that the Validation Qty. be filled in then? I thought this would work: /C^$/  but it doesn't.

<SCRIPT LANGUAGE="JavaScript">

function verify() {
var themessage = "Please enter ";
if (document.AddItem.Part_Number.value !== /C^$/ && document.AddItem.Validation_Qty.value == "") {
themessage = themessage + "Validation Qty.";
}

if (themessage == "Please enter ") {
document.AddItem.submit();
}
else {
alert(themessage);
return false;
   }
  
}

</script>

Andy