How Function works 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: function in c++

#include <iostream>

using namespace std;

void function(){
    cout << "I am a function!" << endl;
}

int main()
{
    function();

    return 0;
}

Example 3: functions in C++

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

int main () {
  Hello();
}