C# for Loop : A Tutorial

The for loop in C# is a control structure that allows repeated execution of a block of code a fixed number of times.

It is commonly used when the number of iterations is known before the loop starts.

This tutorial covers:

• Syntax of the for Loop
• How the for Loop Works
• Example Usage of for Loop
• Using break and continue in a for Loop
• Nested for Loops
• The for Loop with Arrays and Lists
• Best Practices for Using for Loops

1. Syntax of the for Loop

The for loop consists of three parts:

1. Initialization – Declares and initializes a loop variable.
2. Condition – Checks if the loop should continue.
3. Iteration Statement – Updates the loop variable after each iteration.

Syntax

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

2. How the for Loop Works

1. Initialization runs once before the loop starts.
2. Condition is checked before each iteration.
   • If true, the loop body executes.
   • If false, the loop exits.
3. Iteration Statement updates the loop variable.
4. The process repeats until the condition becomes false.

Example: Basic for Loop

for (int i = 1; i <= 5; i++)
{
    Console.WriteLine("Iteration " + i);
}

Output:

Iteration 1
Iteration 2
Iteration 3
Iteration 4
Iteration 5

• int i = 1; → Loop starts with i = 1.
• i <= 5; → Runs while i is less than or equal to 5.
• i++ → Increments i by 1 after each iteration.

3. Example Usage of for Loop

Counting Down Using a for Loop

for (int i = 5; i > 0; i--)
{
    Console.WriteLine("Countdown: " + i);
}
Console.WriteLine("Liftoff!");

Output:

Countdown: 5
Countdown: 4
Countdown: 3
Countdown: 2
Countdown: 1
Liftoff!

• The loop starts from 5 and decrements until it reaches 1.

Skipping Numbers in a for Loop

for (int i = 0; i <= 10; i += 2)
{
    Console.WriteLine(i);
}

Output:

0
2
4
6
8
10

• The loop increments by 2 instead of 1.

4. Using break and continue in a for Loop

Using break to Exit the Loop Early

The break statement terminates the loop immediately when a condition is met.

for (int i = 1; i <= 10; i++)
{
    if (i == 5)
    {
        Console.WriteLine("Stopping loop at " + i);
        break; // Exits the loop when i == 5
    }
    Console.WriteLine(i);
}

Output:

1
2
3
4
Stopping loop at 5

• The loop exits when i == 5.

Using continue to Skip an Iteration

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

for (int i = 1; i <= 5; i++)
{
    if (i == 3)
    {
        Console.WriteLine("Skipping " + i);
        continue; // Skips iteration when i == 3
    }
    Console.WriteLine(i);
}

Output:

1
2
Skipping 3
4
5

• The loop skips i = 3 but continues running.

5. Nested for Loops

A for loop can be placed inside another for loop. This is useful for working with multi-dimensional data, such as matrices.

Example: Printing a Multiplication Table

for (int i = 1; i <= 3; i++)
{
    for (int j = 1; j <= 3; j++)
    {
        Console.Write(i * j + "\t");
    }
    Console.WriteLine();
}

Output:

1   2   3
2   4   6
3   6   9

• The outer loop controls the rows.
• The inner loop controls the columns.

6. The for Loop with Arrays and Lists

The for loop is commonly used to iterate through arrays and lists.

Example: Iterating Through an Array

int[] numbers = { 10, 20, 30, 40, 50 };

for (int i = 0; i < numbers.Length; i++)
{
    Console.WriteLine(numbers[i]);
}

Output:

10
20
30
40
50

• numbers.Length returns the size of the array.
• The loop runs from index 0 to Length – 1.

Example: Iterating Through a List

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List<string> names = new List<string> { "Alice", "Bob", "Charlie" };

        for (int i = 0; i < names.Count; i++)
        {
            Console.WriteLine(names[i]);
        }
    }
}

Output:

Alice
Bob
Charlie

• names.Count returns the number of elements in the list.

7. Best Practices for Using for Loops

Use a for Loop When the Number of Iterations is Known

for (int i = 0; i < 10; i++) { }

• for loops are best when the number of iterations is predefined.

Use Descriptive Variable Names

for (int counter = 0; counter < 5; counter++)

• Avoid using i, j, k unless necessary.
• Use meaningful names for readability.

Use break and continue Wisely

for (int i = 0; i < 10; i++)
{
    if (i % 2 == 0) continue; // Skip even numbers
}

• Use break to exit early and continue to skip iterations.

Avoid Infinite Loops

for (int i = 1; i > 0; i++) { } // Infinite loop

• Always ensure loop conditions will eventually become false.

Use foreach for Collections Instead of for

List<int> numbers = new List<int> { 1, 2, 3 };

foreach (int num in numbers)
{
    Console.WriteLine(num);
}

• foreach is simpler for iterating collections.

Conclusion

• The for loop is used when the number of iterations is known.
• It consists of an initialization, condition, and iteration statement.
• The break statement stops execution, while continue skips an iteration.
• Nested loops handle multi-dimensional data.
• Use for loops with arrays and lists when indexing is required.