Function in C that accepts one input parameter and returns a float number

Create your own function in C that accepts one input parameter and returns a float number. You decide the theme.
You should provide both your C code and an example call to the C code function. Be sure to provide an overview of what your function is doing.
Provide a screen capture showing the results of testing your code in an online compiler. Be sure to test your code with several test cases and show your test case table.