how to use other function element in c++ code example

Example 1: how to declare a function in c++

// function example
#include <iostream>
using namespace std;

int addition (int a, int b)
{
  int r;
  r=a+b;
  return r;
}

Example 2: functions in C++

void Hello() {
  std::cout << "Hello";
}

int main () {
  Hello();
}