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Activity 2.10 Nested Loops

Introduction

In this lesson, we’ll explore the concept of nested loops in C#. Nested loops are tools for handling tasks that involve multiple layers of repetition. By placing one loop inside another, you can manage more complex operations efficiently. In computer science education, nested loops are both challenging and legendary. Each time the outer loop runs, the inner loop completes all its iterations. When tracing nested loops, take your time—it’s easy to get lost in the iterations.

Note, you can nest with any kind of loop, but we will be practicing with for loops.

Example Use Cases

Example

for (int row = 1; row <= 5; row++)
{
	for (int col = 1; col <= 3; col++)
	{
        Console.Write($"[Row {row}, Col {col}]\t");
	}

    Console.WriteLine();
}

[Row 1, Col 1]  [Row 1, Col 2]  [Row 1, Col 3]
[Row 2, Col 1]  [Row 2, Col 2]  [Row 2, Col 3]
[Row 3, Col 1]  [Row 3, Col 2]  [Row 3, Col 3]
[Row 4, Col 1]  [Row 4, Col 2]  [Row 4, Col 3]
[Row 5, Col 1]  [Row 5, Col 2]  [Row 5, Col 3]

Example Video

Table Data: Single For loop or Nested For Loop?

Use a plain for loop when you need to iterate through a single set of data and print out each item. For example, if you’re listing numbers 1 to 10 and their squares, one for loop is enough.

A nested for loop comes in handy when you need to work with two-dimensional data, like a grid or table where each cell represents a combination of two different sets of data. For example, if you’re creating a table that displays Celsius values and their Fahrneheit equivalents:

Console.WriteLine("Celsius\tFahrenheit");
Console.WriteLine("-------------------");

for (int celsius = 0; celsius <= 100; celsius += 10)
{
    for (int increment = 0; increment < 1; increment++)
    {
        double fahrenheit = (celsius * 9 / 5) + 32;
        Console.WriteLine($"{celsius}\t{fahrenheit}");
    }
}

Output

Celsius Fahrenheit
-------------------
0       32
10      50
20      68
30      86
40      104
50      122
60      140
70      158
80      176
90      194
100     212

Skills to Practice

Instructions

Setup

  1. Create a new C# console application. Name the project 2.10 Multiplication Table.
  2. Click Create.

Code

Console.WriteLine("--- Multiplication Table ---");
Console.Write("What number do you want to multiply up to? ");
int max = Convert.ToInt32(Console.ReadLine());
Console.WriteLine();

// Header row
for (int i = 0; i <= max; i++)
{
    // Color top row and left column to distinguish them
    Console.ForegroundColor = ConsoleColor.DarkGreen;

    // Exclude zero at top left
    if (i == 0)
    {
        Console.Write("\t"); // Tab space for alignment
    }
    else
    {
        Console.Write($"{i}\t"); // Use \t for spacing
    }
}

Console.WriteLine();

for (int n1 = 1; n1 <= max; n1++)
{
    // Left column
    Console.ForegroundColor = ConsoleColor.DarkGreen;
    Console.Write($"{n1}\t");
    Console.ForegroundColor = ConsoleColor.White;

    // Body for each row
    for (int n2 = 1; n2 <= max; n2++)
    {
        Console.Write($"{n1 * n2}\t"); // Use \t for spacing
    }

    Console.WriteLine();
}

Debug

Note: The green console color won’t display in the example below, but it will work in an actual terminal.

--- Multiplication Table ---
What number do you want to multiply up to? 5

        1       2       3       4       5
1       1       2       3       4       5
2       2       4       6       8       10
3       3       6       9       12      15
4       4       8       12      16      20
5       5       10      15      20      25

Tips, Tricks, and Reflection