How do I write this line of code in a more readable manner?

Problem: " Write a C++ program to create a new string of the characters at indexes 0,1, 4,5, 8,9 … from a given string. "

Solution (not mine):

#include <iostream>
 
using namespace std;

string test(string str1)
          {
           string result = "";
            for (int i = 0; i < str1.length(); i += 4)
            {
                int c = i + 2;
                int n = 0;
                n += c > str1.length() ? 1 : 2;
                result += str1.substr(i, n);
            }
            return result;
        }
        
int main() 
 {
  cout << test("Python") << endl; 
  cout << test("JavaScript") << endl; 
  cout << test("HTML") << endl;     
  return 0;    
} 

Whenever I cannot understand some code, I would just do every step on paper by hand, until I understand what it actually does.

This time, I can’t really figure out this line:

n += c > str1.length() ? 1 : 2;

I would appreciate if anyone could write this line in a more clear, beginner-friendly manner.

Thank you for your time.

>Solution :

I can’t really figure out this line: n += c > str1.length() ? 1 : 2;

This uses the conditional operator and checks the condition that whether c is greater than str1.length() and if so then it is as if we’re doing n+=1 while if the condition is not satisfied then it is as if we’re doing n+=2.

Basically the same as:

if(n > str.length())
{
   n+=1;
}
else 
{
   n+=2;
}