Minor clean up for cooley tukey in C++
Minor clean up for cooley tukey in C++

- rename c64 to complex
- make pi a constant instead of function
- fix complilation warnings about comparing signed int with unsigned int

leios/algorithm-archive,leios/algorithm-archive,leios/algorithm-archive,Gathros/algorithm-archive,leios/algorithm-archive,leios/algorithm-archive,Gathros/algorithm-archive,Gathros/algorithm-archive,leios/algorithm-archive,Gathros/algorithm-archive,leios/algorithm-archive,leios/algorithm-archive,Gathros/algorithm-archive,leios/algorithm-archive,leios/algorithm-archive,Gathros/algorithm-archive,leios/algorithm-archive,leios/algorithm-archive,Gathros/algorithm-archive,leios/algorithm-archive,Gathros/algorithm-archive,Gathros/algorithm-archive,leios/algorithm-archive,Gathros/algorithm-archive,leios/algorithm-archive,leios/algorithm-archive,Gathros/algorithm-archive,Gathros/algorithm-archive,Gathros/algorithm-archive,Gathros/algorithm-archive,Gathros/algorithm-archive,leios/algorithm-archive,leios/algorithm-archive,Gathros/algorithm-archive