I won't answer your question, but I will show you how to answer it yourself. This is a fundamental skill for any 'C' programmer:

Ever since Kernighan & Ritchie first published their 'C' programming language, there has been a standard library defined to go with it.

The Standard Library contains a whole load of functions for doing all sorts of useful things.

Therefore, your first step must be to look-up the section on the Standard Library in your 'C' textbook, and see which one(s) fit your requirements.

You will find what you require there.

You will also have to check in your compiler Manual for any implementaiton-specific details, limitations, restrictions, etc.


To start with, you will probably have to do this daily; as your experience grows, you will come to remember your most commonly used library functions, and will only have to search when an unusual requirement comes along.
But you need to practise doing it!