Answer 1

Please show, what u have done so far.

Answer 2

Try to transform into string the inputed value. For example let's say input is 20923 ok? Take this string "20923" (or if its number 20923 make it string , int.toString()) and start from right to left counting digits. Every 3 digits you put a comma. Tell me what language do you need in order to help you furthermore.