#include <iostream>

int a;

void increase(int& a)
{
    a++;
    return;
}


int& increase()
{
    a++;
    return a;
}

int main()
{
    std::cout<<"Before calling function: " <<a<<std::endl;
    increase(a);
    std::cout<<"After calling function with parameter: " <<a<<std::endl;
    a = increase();
    std::cout<<"After calling function returns reference: " <<a<<std::endl;
    
    return 0;
}