Fibonacci sequence program

[GolamMostafa]

@cotestatnt

it would have been better if the OP had come up with the algorithm using his skills and knowledge.

I agree with you fully; but, sometimes OP needs an example which may prompt him to ask inquisitive questions. I have reason to believe that OP has no idea about recursion (a difficult concept to digest how a program does call itself!); let's see if he asks question what is a recursion.

@cotestatnt

However, in my opinion the unsigned long sum local variable is redundant. You can return the result of the sum directly.

I have avoided nested codes for the convenience of reading.