C# Loops

Loops are fundamental programming constructs that allow you to execute a block of code repeatedly. In C#, loops are essential for tasks like processing collections of data, implementing repetitive calculations, or executing code until a specific condition is met.

Introduction to Loops

In programming, we often need to perform the same action multiple times. Instead of writing the same code over and over again, we use loops to repeat actions. C# provides several types of loops, each with its own use cases:

for loops: Used when you know exactly how many times you want to loop
foreach loops: Designed for iterating over collections like arrays and lists
while loops: Execute as long as a condition remains true
do-while loops: Similar to while loops but guarantee at least one execution

Let's explore each type of loop in detail.

The `for` Loop

The for loop is one of the most common loops in C#. It's particularly useful when you know the exact number of iterations needed.

Syntax

csharp
for (initialization; condition; iteration)
{
    // Code to be executed
}

The for loop consists of three parts:

Initialization: Executed once at the beginning
Condition: Checked before each iteration; the loop continues as long as it's true
Iteration: Executed after each iteration

Example: Counting from 1 to 5

csharp
using System;

class Program
{
    static void Main()
    {
        for (int i = 1; i <= 5; i++)
        {
            Console.WriteLine($"Count: {i}");
        }
    }
}

Output:

Count: 1
Count: 2
Count: 3
Count: 4
Count: 5

In this example:

int i = 1 initializes the counter variable
i <= 5 sets the condition to continue looping
i++ increments the counter after each iteration

Practical Application: Calculating Factorial

csharp
using System;

class Program
{
    static void Main()
    {
        int number = 5;
        int factorial = 1;
        
        for (int i = 1; i <= number; i++)
        {
            factorial *= i;
        }
        
        Console.WriteLine($"The factorial of {number} is: {factorial}");
    }
}

Output:

The factorial of 5 is: 120

The `foreach` Loop

The foreach loop is designed specifically for iterating through collections like arrays, lists, and other enumerable objects.

Syntax

csharp
foreach (type item in collection)
{
    // Code to be executed for each item
}

Example: Iterating Through an Array

csharp
using System;

class Program
{
    static void Main()
    {
        string[] fruits = { "Apple", "Banana", "Cherry", "Date", "Elderberry" };
        
        foreach (string fruit in fruits)
        {
            Console.WriteLine($"Current fruit: {fruit}");
        }
    }
}

Output:

Current fruit: Apple
Current fruit: Banana
Current fruit: Cherry
Current fruit: Date
Current fruit: Elderberry

Unlike the for loop, foreach doesn't require you to manage indexes or check boundaries, making your code cleaner and less prone to errors when working with collections.

Practical Application: Calculating Average of Scores

csharp
using System;

class Program
{
    static void Main()
    {
        int[] scores = { 85, 92, 78, 95, 88 };
        int sum = 0;
        
        foreach (int score in scores)
        {
            sum += score;
        }
        
        double average = (double)sum / scores.Length;
        Console.WriteLine($"The average score is: {average}");
    }
}

Output:

The average score is: 87.6

The `while` Loop

The while loop executes a block of code as long as a specified condition is true. It checks the condition before each iteration.

Syntax

csharp
while (condition)
{
    // Code to be executed
}

Example: Counting Down from 5

csharp
using System;

class Program
{
    static void Main()
    {
        int countdown = 5;
        
        while (countdown > 0)
        {
            Console.WriteLine($"Countdown: {countdown}");
            countdown--;
        }
        
        Console.WriteLine("Blast off!");
    }
}

Output:

Countdown: 5
Countdown: 4
Countdown: 3
Countdown: 2
Countdown: 1
Blast off!

The while loop is particularly useful when you don't know in advance how many iterations you'll need.

Practical Application: Reading User Input Until a Condition

csharp
using System;

class Program
{
    static void Main()
    {
        string input = "";
        
        while (input != "exit")
        {
            Console.Write("Enter a command (type 'exit' to quit): ");
            input = Console.ReadLine();
            Console.WriteLine($"You entered: {input}");
        }
        
        Console.WriteLine("Program terminated.");
    }
}

Output (example interaction):

Enter a command (type 'exit' to quit): hello
You entered: hello
Enter a command (type 'exit' to quit): C#
You entered: C#
Enter a command (type 'exit' to quit): exit
You entered: exit
Program terminated.

The `do-while` Loop

The do-while loop is similar to the while loop, with one key difference: it checks the condition after the code block executes, guaranteeing at least one execution of the code.

Syntax

csharp
do
{
    // Code to be executed
} while (condition);

Example: Basic `do-while` Loop

csharp
using System;

class Program
{
    static void Main()
    {
        int i = 1;
        
        do
        {
            Console.WriteLine($"Iteration: {i}");
            i++;
        } while (i <= 5);
    }
}

Output:

Iteration: 1
Iteration: 2
Iteration: 3
Iteration: 4
Iteration: 5

Practical Application: Input Validation

csharp
using System;

class Program
{
    static void Main()
    {
        int number;
        
        do
        {
            Console.Write("Enter a positive number: ");
            number = Convert.ToInt32(Console.ReadLine());
            
            if (number <= 0)
            {
                Console.WriteLine("That's not a positive number. Please try again.");
            }
        } while (number <= 0);
        
        Console.WriteLine($"You entered the positive number: {number}");
    }
}

Output (example interaction):

Enter a positive number: -5
That's not a positive number. Please try again.
Enter a positive number: 0
That's not a positive number. Please try again.
Enter a positive number: 10
You entered the positive number: 10

Control Statements in Loops

C# provides special statements to alter the normal flow of loops:

`break` Statement

The break statement immediately exits the loop, regardless of the condition.

csharp
using System;

class Program
{
    static void Main()
    {
        for (int i = 1; i <= 10; i++)
        {
            if (i == 6)
            {
                Console.WriteLine("Breaking the loop at i = 6");
                break;
            }
            Console.WriteLine($"Current value: {i}");
        }
        Console.WriteLine("Loop finished");
    }
}

Output:

Current value: 1
Current value: 2
Current value: 3
Current value: 4
Current value: 5
Breaking the loop at i = 6
Loop finished

`continue` Statement

The continue statement skips the current iteration and moves to the next one.

csharp
using System;

class Program
{
    static void Main()
    {
        for (int i = 1; i <= 5; i++)
        {
            if (i == 3)
            {
                Console.WriteLine("Skipping iteration for i = 3");
                continue;
            }
            Console.WriteLine($"Current value: {i}");
        }
    }
}

Output:

Current value: 1
Current value: 2
Skipping iteration for i = 3
Current value: 4
Current value: 5

Nested Loops

You can place loops inside other loops, creating nested loops. This is useful for working with multi-dimensional data structures.

csharp
using System;

class Program
{
    static void Main()
    {
        int rows = 3;
        int columns = 4;
        
        for (int i = 0; i < rows; i++)
        {
            for (int j = 0; j < columns; j++)
            {
                Console.Write($"({i},{j}) ");
            }
            Console.WriteLine(); // Move to the next line after each row
        }
    }
}

Output:

(0,0) (0,1) (0,2) (0,3) 
(1,0) (1,1) (1,2) (1,3) 
(2,0) (2,1) (2,2) (2,3) 

Practical Application: Printing a Pattern

csharp
using System;

class Program
{
    static void Main()
    {
        int rows = 5;
        
        for (int i = 1; i <= rows; i++)
        {
            for (int j = 1; j <= i; j++)
            {
                Console.Write("* ");
            }
            Console.WriteLine();
        }
    }
}

Output:

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

Infinite Loops

Sometimes we need a loop to run indefinitely until an explicit break condition. This is called an infinite loop.

csharp
using System;

class Program
{
    static void Main()
    {
        int count = 0;
        
        while (true)
        {
            Console.WriteLine($"Iteration: {count}");
            count++;
            
            if (count >= 5)
            {
                Console.WriteLine("Breaking out of the infinite loop");
                break;
            }
        }
    }
}

Output:

Iteration: 0
Iteration: 1
Iteration: 2
Iteration: 3
Iteration: 4
Breaking out of the infinite loop

Be careful with infinite loops! Always ensure there's a way to exit the loop.

Summary

Loops are powerful constructs in C# that allow you to execute code repeatedly based on specific conditions:

for loops: Best when you know the exact number of iterations needed
foreach loops: Ideal for iterating through collections like arrays and lists
while loops: Perfect when you need to continue execution until a condition becomes false
do-while loops: Similar to while loops but guarantees at least one execution

Choosing the right loop depends on your specific requirements:

Use for when you need precise control over the iteration process
Use foreach for clean and safe iteration through collections
Use while when the number of iterations is indeterminate
Use do-while when you need to guarantee at least one execution

Understanding loops and how to control them with break and continue statements is essential for writing efficient C# programs.

Exercises

Write a program that uses a for loop to print all even numbers between 1 and 20.
Create an array of your favorite movies and use a foreach loop to display them.
Write a program using a while loop that asks the user to guess a number between 1 and 10.
Use a do-while loop to create a simple calculator that continues to run until the user chooses to exit.
Create a nested loop to print a multiplication table for numbers 1 through 5.

Additional Resources

Happy coding!

If you spot any mistakes on this website, please let me know at [email protected]. I’d greatly appreciate your feedback! :)

Introduction to Loops​

The for Loop​

Syntax​

Example: Counting from 1 to 5​

Practical Application: Calculating Factorial​

The foreach Loop​

Syntax​

Example: Iterating Through an Array​

Practical Application: Calculating Average of Scores​

The while Loop​

Syntax​

Example: Counting Down from 5​

Practical Application: Reading User Input Until a Condition​

The do-while Loop​

Syntax​

Example: Basic do-while Loop​

Practical Application: Input Validation​

Control Statements in Loops​

break Statement​

continue Statement​

Nested Loops​

Practical Application: Printing a Pattern​

Infinite Loops​

Summary​

Exercises​

Additional Resources​

Introduction to Loops

The `for` Loop

Syntax

Example: Counting from 1 to 5

Practical Application: Calculating Factorial

The `foreach` Loop

Syntax

Example: Iterating Through an Array

Practical Application: Calculating Average of Scores

The `while` Loop

Syntax

Example: Counting Down from 5

Practical Application: Reading User Input Until a Condition

The `do-while` Loop

Syntax

Example: Basic `do-while` Loop

Practical Application: Input Validation

Control Statements in Loops

`break` Statement

`continue` Statement

Nested Loops

Practical Application: Printing a Pattern

Infinite Loops

Summary

Exercises

Additional Resources