Chapter 6.1. Nested Loops

In the current chapter we will be looking at nested loops and how to use for loops to draw various figures on the console, that contain symbols and signs, ordered in rows and columns on the console. We will use single and nested loops (loops that stay in other loops), calculations and checks, in order to print on the console simple and not so simple figures by specified sizes.

Video: Chapter Overview

Watch a video lesson to learn what we will learn in this chapter: https://youtu.be/sbmhyr1Yz7U.

Introduction to Nested Loops by Examples

In programming loops can be nested, which means that in a loop we can put another loop. This is an example of nested for-loops, which are used to draw a square of n rows, each holding n times the chars =-:

int n = int.Parse(Console.ReadLine());
for (int row = 1; row <= n; row++)
{
    for (int col = 1; col <= n; col++)
    {
        Console.Write("=-");
    }
    Console.WriteLine();
}

Run the above code example: https://repl.it/@nakov/nested-for-loops-draw-square-csharp.

If we run the above code and enter 5 as input, the output will be as follows:

5
=-=-=-=-=-
=-=-=-=-=-
=-=-=-=-=-
=-=-=-=-=-
=-=-=-=-=-

Using a combination of calculations, conditional statements and nested loops, we can implement more complex logic. For example, we can draw a rhombus of stars as follows:

int n = 10;
for (int row = 1; row < n; row++)
{
    var spaces = Math.Abs(n / 2 - row);
    var stars = n/2 - spaces;
    for (int col = 1; col <= spaces; col++)
        Console.Write(" ");
    for (int col = 1; col <= stars; col++)
        Console.Write("* ");
    Console.WriteLine();
}

Run the above code example: https://repl.it/@nakov/nested-for-loops-draw-rhombus-csharp.

The above code will print on the console the following output:

    *
   * *
  * * *
 * * * *
* * * * *
 * * * *
  * * *
   * *
    *

Let's explain in greater detail how to use nested loops to implement more complex logic in our C# programs.