Understanding Looping

[siriusly]

Hello I'm new to C++. This is my second time writing a program.
I'm supposed to write this code where if i input an even number, a loop based triangle shows up and if i input an odd number, a different loop based triangle shows up. I got some help from a website and modified it for my needs and it works perfectly. The only problem is that I don't understand how it works.

  #include <iostream>

using namespace std;

int main()
{
    int input;
    cin >> input;
    if (input %2 == 0 && input > 0) {

  for( int i = 6; i >= 1; i-- )
  {
    for( int j = 1; j <= 6; j++)
    {
      cout << (j <= i ? "*" : " " );
    }
    cout << endl;
  }
  }

if (input %2 == 1 && input > 0 )
    {

  for( int i = 1; i <= 6; i++ )
  {
    for( int j = 1; j <= 6; j++)
    {
      cout << (j <= i ? "*" : " " );
    }
    cout << endl;
  }



   return 0;
}
}

why do i have two integers? why won't it work if i just put in i alone or j alone?

Thank you for your time.

[crimsonzero2]

Basically, the inner for loop is printing out the "*" while the outside loop allows the program to go to the next line for the inner loop to redo the process.

[TheKingOfTyrants]

Think about what you're doing: you're printing a 2D triangle, so you need to keep track of both an X/row and Y/column coordinate.

[siriusly]

I am going to sound dumb but I still don't get it.

[crimsonzero2]

Think of the outer loop being the row you are editing. As you get into a row, the inner loop will do something with that row (in this case print out a number of "*"). Once the inner loop is finished, the outer loop would then go to the next row and keep doing this until the outer loop is completed.