C# for loop

Summary: in this tutorial, you’ll learn how to use the C# for loop statement to execute a block repeatedly.

Introduction to the C# for loop statement #

C# for statement executes a block while a condition is true. The following shows the syntax of the for statement:

for(initializer; condition; iterator)
{
    // statement
}

The for statement has the following elements initializer, condition, iterator, and the loop body

initializer #

The for statement executes the initializer only once before entering the loop. Typically, you declare and initialize a local loop variable in the initializer.

Note that if you declare a variable in the initializer, you cannot access it outside the for statement.

condition #

The condition is a boolean expression that determines whether the for statement should execute the next iteration.

The for statement evaluates the condition before each iteration. If the condition is true (or is not present), the for statement executes the next iteration. Otherwise, it’ll exit the loop.

iterator #

The for statement executes the iterator after each iteration.

loop body #

The loop body is inside the curly braces ({}) that may consist of one or more statements. If the condition is true (or not present), the for statement executes the loop body in each iteration.

In the for statement, the initializer, condition, and iterator are optional. Therefore, you can have an indefinite for loop like this:

for(;;) 
{
    // statement
}

In this case, you need to use the break statement to terminate the loop at some point in time to avoid an indefinite loop.

The following flowchart illustrates how the for loop statement works.

In practice, you’ll use the for statement to execute a block a specified number of times.

C# for loop examples #

Let’s take some examples of using the for loop statement.

1) A simple C# for loop example #

The following example uses the for statement to output three numbers from zero to two to the console:

for (int i = 0; i < 3; i++)
{
    Console.WriteLine(i);
}

Output:

0
1
2

How it works.

In the initializer, we declare and initialize the local variable i:

int i = 0

In this condition, we check if the variable i is less than three. The condition will determine if the next iteration should run:

i < 3

Since the variable i is zero, which is less than three, the for statement executes its loop body that outputs the variable i to the console:

Console.WriteLine(i);

After the first iteration, the for statement runs the iterator that increases the value of the variable i by one:

i++

The i variable is 1.

Starting from the second iteration, the for statement doesn’t execute the initializer but only evaluates the condition to determine whether it should continue to the next iteration.

i < 3

Because the variable i is one, the condition is true. Therefore, the for statement executes its loop body the second time that outputs the variable i to the console, and executes the iterator that increases the variable i by one:

i++

After this, the variable i is two. The for statement continues checking the condition to determine if it should continue to the next iteration:

i < 3

Because variable i is two, the condition is true. Therefore, the for statement runs the third iteration that outputs the variable i to the output and increases the variable i by one.

This time the i variable is three that made the condition false. Hence, the loop exits.

In summary, the for statement runs its body three times that output three numbers zero, one, and two to the console.

2) Using the C# for loop to calculate the total of integers from 1 to 10 #

The following example uses the C# for statement to calculate the total of integers from 1 to 10:

int total = 0;
for (int i = 1; i <= 10; i++)
{
    total += i;

}
Console.WriteLine($"Total:{total}");

Output:

Total:55

In this example, the for statement adds the variable i to the total in each iteration.

3) Using the C# for loop to display even numbers in the range #

The following example uses the for loop statement to display even numbers between 0 and 10:

for (int i = 0; i < 10; i++)
{
    if (i % 2 == 0)
    {
        Console.Write($"{i} ");
    }
}

Output:

0 2 4 6 8

In this example, the loop body only displays the variable i if it is an even number determined by the condition i%2 == 0.

4) Using the C# for loop to display every character of a string #

The following example uses the for statement to display every character of a string:

string message = "Hello";

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

Output:

H
e
l
l
o

In this example, the string message has an index starting from 0 to message.Length - 1. Therefore, we use the for statement to access individual characters of the string by an index in that range.

Summary #

Use the for loop to execute a block repeatedly for a specified number of times.

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