undefined reference to <function name=""> in the same project file

Question

I'm using codeblocks IDE and I don't know what is the problem.

I tried making the variables global but it still doesn't work.

Answer 1

The problem is in the function name. Calculate_area has a capital 'C' in its function declaration name, but not in the prototype declaration.

Change your function declaration at line 31 with:

unsigned long calculate_area(unsigned long side);