C++ arithmetic & decrement operator

Write a program that generates the following output:

   10

   20

   30

 Use an integer constant for the 10, an arithmetic assignment operator to generate the 20, and a decrement operator to generate 19.

CODE:

#include <iostream>
/*  Author: Danial Ahmed
    Website: http://program-cpp.blogspot.com/
    Contact: danyalphc@gmail.com */
using namespace std;
int main(){
    int kons=10;
    int r1=2*kons, r2=r1-1;
    cout << kons << endl << r1 << endl << r2 << endl;
    return 0;
}

OUTPUT: