is_int with HTML FORM

Hey there, First of all please CC me as I'm no longer a member on this list. Sorry about that but I receive too much :-(. Please bear with me as I'm a new PHP scripter on the block.... Ok for the question. I was under the impression that PHP would automatically select the type for the vars to use. However if I have a field in my form where I insert only a 4 in I'd expect the var to be an integer (or atleast some other whole number type of var). However is_int fails on the 4 and sees it as a string. So how am I going to check whether it's nothing but digits [0-9]. The field can hold 4 characters but they don't neccesarily need to be filled. So the input could be 1 through 9999. Now I could check with > or < but that won't work since they would still eval true if they'd enter 3a. Ok it would fail if they'd enter a3 but that still leaves a possibility to crash my script with 3a. Perhaps somebody could hand me a nice regexp or something... I'm not yet familiar with those. Kind regards and have a nice weekend. Ferry van Steen