[SOLVED] How to determine if the user input a STRING or an INTEGER?

Is there a way to know if the user input a STRING or an INTEGER?

Example: 1, 2, 3, 4, 5

(NO DECIMAL PLACES)

I have an input box that the user will input a number only and I don't want the user input a string or something that not related to integer data type. I mean I need a validation that will determine the user input a string or something not related to integer.