c++ header files example
//headers
#ifndef TOOLS_hpp
#define TOOLS_hpp
#include<vector>
#include<iostream>
#include<fstream>
#include<string>
using std::ifstream;
using std::cout;
using std::cin;
using std::endl;
using std::cerr;
using std::vector;
using std::string;
// functions prototypes
inline vector<int> merge(const vector<int>&a,const vector<int>& b);//merge function prototype with Formal Parameters
std::vector<int> sort(size_t start, size_t length, const std::vector<int>& vec);//sort function prototype with formal parameters
#endif