C# For Loop

Introduction

The for loop is one of the most commonly used control flow statements in C#. It allows you to execute a block of code repeatedly for a specific number of times. For loops are particularly useful when you know in advance how many times you want to iterate through a block of code.

In this tutorial, you'll learn:

The syntax and structure of the C# for loop
How to create and use for loops
Common patterns and techniques
Real-world applications

Basic Syntax

The syntax of a for loop in C# consists of three main parts:

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

Let's examine each part:

Initialization: Executes once at the beginning of the loop. Typically used to declare and initialize a counter variable.
Condition: Evaluated before each iteration. If true, the loop continues; if false, the loop ends.
Iteration: Executes after each iteration. Usually increments or decrements the counter.

Basic For Loop Example

Here's a simple example that counts 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 a counter variable i with the value 1
i <= 5 specifies that the loop should continue as long as i is less than or equal to 5
i++ increments the counter by 1 after each iteration

Variations of For Loops

Counting Backwards

You can count backwards by decrementing the counter:

csharp
for (int i = 10; i > 0; i--)
{
    Console.WriteLine($"Countdown: {i}");
}
Console.WriteLine("Blast off!");

Output:

Countdown: 10
Countdown: 9
Countdown: 8
Countdown: 7
Countdown: 6
Countdown: 5
Countdown: 4
Countdown: 3
Countdown: 2
Countdown: 1
Blast off!

Custom Increments

You're not limited to incrementing by 1. You can use any increment you want:

csharp
// Count by 2s (even numbers)
for (int i = 0; i <= 10; i += 2)
{
    Console.WriteLine($"Even number: {i}");
}

Output:

Even number: 0
Even number: 2
Even number: 4
Even number: 6
Even number: 8
Even number: 10

Multiple Variables

You can use multiple variables in a for loop:

csharp
for (int i = 1, j = 10; i <= 5; i++, j--)
{
    Console.WriteLine($"i = {i}, j = {j}");
}

Output:

i = 1, j = 10
i = 2, j = 9
i = 3, j = 8
i = 4, j = 7
i = 5, j = 6

Advanced For Loop Techniques

Nested For Loops

You can place a for loop inside another for loop, creating nested loops:

csharp
for (int i = 1; i <= 3; i++)
{
    for (int j = 1; j <= 3; j++)
    {
        Console.WriteLine($"i = {i}, j = {j}");
    }
    Console.WriteLine("----------");
}

Output:

i = 1, j = 1
i = 1, j = 2
i = 1, j = 3
----------
i = 2, j = 1
i = 2, j = 2
i = 2, j = 3
----------
i = 3, j = 1
i = 3, j = 2
i = 3, j = 3
----------

Break and Continue Statements

You can control the flow within a for loop using break and continue statements:

break: Exits the loop immediately
continue: Skips the current iteration and moves to the next one

csharp
for (int i = 1; i <= 10; i++)
{
    if (i == 3)
    {
        Console.WriteLine("Skipping 3...");
        continue; // Skip the rest of this iteration
    }
    
    if (i == 8)
    {
        Console.WriteLine("Found 8! Breaking the loop.");
        break; // Exit the loop
    }
    
    Console.WriteLine($"Number: {i}");
}

Output:

Number: 1
Number: 2
Skipping 3...
Number: 4
Number: 5
Number: 6
Number: 7
Found 8! Breaking the loop.

Empty Parts in For Loop

Any part of the for loop can be omitted if needed:

csharp
// Initialize outside the loop
int i = 1;
for (; i <= 5; i++)
{
    Console.WriteLine(i);
}

// Omitting the increment (handle inside the loop)
for (int j = 1; j <= 5;)
{
    Console.WriteLine(j);
    j++;
}

// Creating an infinite loop with break condition
for (;;)
{
    Console.WriteLine("This is an infinite loop!");
    break; // Without this, the loop would run forever
}

Real-World Applications

Iterating Through Arrays

One of the most common uses of for loops is to iterate through arrays:

csharp
string[] fruits = { "Apple", "Banana", "Cherry", "Date", "Elderberry" };

for (int i = 0; i < fruits.Length; i++)
{
    Console.WriteLine($"Fruit at index {i}: {fruits[i]}");
}

Output:

Fruit at index 0: Apple
Fruit at index 1: Banana
Fruit at index 2: Cherry
Fruit at index 3: Date
Fruit at index 4: Elderberry

Building String Patterns

For loops are great for building patterns:

csharp
// Create a simple triangle pattern
for (int i = 1; i <= 5; i++)
{
    for (int j = 1; j <= i; j++)
    {
        Console.Write("*");
    }
    Console.WriteLine();
}

Output:

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

Calculating Values

For loops are useful for calculations like factorial:

csharp
int number = 5;
int factorial = 1;

for (int i = 1; i <= number; i++)
{
    factorial *= i;
}

Console.WriteLine($"Factorial of {number} is {factorial}");

Output:

Factorial of 5 is 120

For Loop vs. Other Loops

It's worth noting when a for loop is most appropriate compared to other loop types:

For loop: Best when you know the exact number of iterations in advance.
While loop: Better when you don't know how many iterations you'll need.
Foreach loop: Ideal for iterating through collections without needing the index.

Common Pitfalls

Off-by-One Errors

Be careful when setting your loop conditions to avoid off-by-one errors:

csharp
// If we want to go from 0 to 9 (10 numbers):
for (int i = 0; i <= 9; i++) { }  // Correct
for (int i = 0; i < 10; i++) { }  // Also correct
for (int i = 0; i <= 10; i++) { } // Incorrect - goes to 10 (11 numbers)

Infinite Loops

Always ensure your loop condition will eventually become false:

csharp
// Infinite loop (i never decreases)
for (int i = 10; i > 0; i++)
{
    // This will run forever!
}

Summary

The C# for loop is a powerful and flexible control flow statement that allows you to execute a block of code a specific number of times. It consists of initialization, condition, and iteration expressions, which give you fine-grained control over how your loop behaves.

For loops are especially useful when:

You know exactly how many iterations you need
You need to track an index while iterating
You need precise control over the iteration behavior

Throughout this tutorial, we've seen how to create basic for loops, use variations and advanced techniques, and apply them to real-world programming problems.

Exercises

To solidify your understanding, try these exercises:

Write a for loop that displays all even numbers between 20 and 40.
Create a program that uses a for loop to calculate the sum of all numbers from 1 to 100.
Write a nested for loop to create a multiplication table for numbers 1 through 10.
Implement a for loop that finds and displays all factors of a given number.
Create a program that uses a for loop to reverse a string.

Additional Resources

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

Introduction​

Basic Syntax​

Basic For Loop Example​

Variations of For Loops​

Counting Backwards​

Custom Increments​

Multiple Variables​

Advanced For Loop Techniques​

Nested For Loops​

Break and Continue Statements​

Empty Parts in For Loop​

Real-World Applications​

Iterating Through Arrays​

Building String Patterns​

Calculating Values​

For Loop vs. Other Loops​

Common Pitfalls​

Off-by-One Errors​

Infinite Loops​

Summary​

Exercises​

Additional Resources​

Introduction

Basic Syntax

Basic For Loop Example

Variations of For Loops

Counting Backwards

Custom Increments

Multiple Variables

Advanced For Loop Techniques

Nested For Loops

Break and Continue Statements

Empty Parts in For Loop

Real-World Applications

Iterating Through Arrays

Building String Patterns

Calculating Values

For Loop vs. Other Loops

Common Pitfalls

Off-by-One Errors

Infinite Loops

Summary

Exercises

Additional Resources