Arrays It is often convenient in math to have a variable with a subscript to index it. When declaring this variable, we need to say how much room to set aside for it. Mathematical functions C doesn't naturally contain any mathematical functions.
Many systems keep their math functions in a special library.
These take arguments as double's. You can fix this with a cast. If your program outputs anything beyond a few numbers, you will probably want to put its output in a file. The way files are handled varies from system to system, so C wants no part of it. In particular, C doesn't want to tote around names of files or how to access them, so we only make it carry around a number.