do functions need to be in header files cpp code example

Example 1: c++ header files

// You should use header files when you wan't to split your
// program across multiple files. Use it like this:

// vec2.hpp
class vec2 {
	public:
  		void printVec(); // Decleration
  		float x, y;
}
// vec2.cpp
#include "vec2.hpp"
void vec2::printVec() { // Implementation
	std::cout << x << y << std::endl;
}

Example 2: including cpp header file in c++

#include "enter_name_here.cpp"

//Make sure the files are in the same directory.