C# for Loop

Updated on: June 17, 2020

Here, you will learn how to execute a statement or code block multiple times using the for loop, structure of the for loop, nested for loops, and how to exit from the for loop.

The for keyword indicates a loop in C#. The for loop executes a block of statements repeatedly until the specified condition returns false.

Syntax:

for (initializer; condition; iterator)//code block

The for loop contains the following three optional sections, separated by a semicolon:

Initializer: The initializer section is used to initialize a variable that will be local to a for loop and cannot be accessed outside loop. It can also be zero or more assignment statements, method call, increment, or decrement expression e.g., ++i or i++, and await expression.

Condition: The condition is a boolean expression that will return either true or false. If an expression evaluates to true, then it will execute the loop again; otherwise, the loop is exited.

Iterator: The iterator defines the incremental or decremental of the loop variable.

The following for loop executes a code block 10 times.

Example: for Loop

for(int i = 0; i < 10; i++)
{
    Console.WriteLine("Value of i: {0}", i);
}
</code></pre>
        <div className="card-footer example-footer">@ttHelpers.TryItLink("cid=cs-078hIg") </div>
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        Output:
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    <samp>
        Value of i: 0
        <br />
        Value of i: 1
        <br />
        Value of i: 2
        <br />
        Value of i: 3
        <br />
        Value of i: 4
        <br />
        Value of i: 5
        <br />
        Value of i: 6
        <br />
        Value of i: 7
        <br />
        Value of i: 8
        <br />
        Value of i: 9
    </samp>
        <p>In the above example, <code>int i = 0</code> is an initializer where we define an int variable <code>i</code> and initialize it with 0. 
    The second section is the condition expression <code>i < 10</code>, if this condition returns <code>true</code> then it will execute a code block. After executing the code block, it will go to the third section, iterator. 
    The <code>i++</code> is an incremental statement that increases the value of a loop variable <code>i</code> by 1. Now, it will check the conditional expression again and repeat the same thing until conditional expression returns <code>false</code>.
The below figure illustrates the execution steps of the <code>for</code> loop.</p>

    <p>
        The below figure illustrates the execution steps of the <code>for</code> loop.
    </p>

    <ResponsiveImage src="/images/csharp/for-loop.webp" alt="for Loop Execution Steps" priority={true} />
    <p>If a code block only contains a single statement, then you don't need to wrap it inside curly brackets <code>{ }</code>, as shown below. </p>
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<code>for(int i = 0; i < 10; i++)
    Console.WriteLine("Value of i: {0}", i);
</code></pre>
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    <p>
        An Initializer, condition, and iterator sections are optional. You can initialize a variable before <code>for</code> loop, and condition and iterator can be defined inside a code block, as shown below.
    </p>


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        <div className="card-header example-title">Example: for loop C# </div>
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<code>int i = 0;

for(;;)
{
    if (i < 10)
    {
        Console.WriteLine("Value of i: {0}", i);
        i++;
    }
    else
        break;
}

Try it

Output:

Value of i: 0 Value of i: 1 Value of i: 2 Value of i: 3 Value of i: 4 Value of i: 5 Value of i: 6 Value of i: 7 Value of i: 8 Value of i: 9

Since all three sections are optional in the for loop, be careful in defining a condition and iterator. Otherwise, it will be an infinite loop that will never end the loop.

Example: Infinite for Loop

for ( ; ; )
{
    Console.Write(1);
}

Output:

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1.....

The control variable for the for loop can be of any numeric data type, such as double, decimal, etc.

Example: Decimal for Loop

for (double d = 1.01D; d < 1.10; d+= 0.01D)
{
    Console.WriteLine("Value of i: {0}", d);
}

Try it

Output:

Value of i: 1.01 Value of i: 1.02 Value of i: 1.03 Value of i: 1.04 Value of i: 1.05 Value of i: 1.06 Value of i: 1.07 Value of i: 1.08 Value of i: 1.09

The steps part in a for loop can either increase or decrease the value of a variable.

Example: Reverse for Loop

for(int i = 10; i > 0; i--)
{
    Console.WriteLine("Value of i: {0}", i);
}

Try it

Output:

Value of i: 10 Value of i: 9 Value of i: 8 Value of i: 7 Value of i: 6 Value of i: 5 Value of i: 4 Value of i: 3 Value of i: 2 Value of i: 1

Exit the for Loop

You can also exit from a for loop by using the break keyword.

Example: break in for loop

for (int i = 0; i < 10; i++)
{
    if( i == 5 )
        break;

    Console.WriteLine("Value of i: {0}", i);
}

Try it

Output:

Value of i: 0 Value of i: 1 Value of i: 2 Value of i: 3 Value of i: 4

Multiple Expressions

A for loop can also include multiple initializer and iterator statements separated by comma, as shown below.

Example: Multiple Expressions

for (int i = 0, j = 0; i+j < 5; i++, j++)
{
    Console.WriteLine("Value of i: {0}, J: {1} ", i,j);
}

Try it

Output:

Value of i: 0, J: 0 Value of i: 1, J: 1 Value of i: 2, J: 2

A for loop can also contain statements as an initializer and iterator.

Example: Initializer and Iterator Statements

int i = 0, j = 5;
for (Console.WriteLine($"Initializer: i={i}, j={j}"); 
    i++ < j--; 
    Console.WriteLine($"Iterator: i={i}, j={j}"))
    {
    }

Try it

Output:

Initializer: i=0, j=5 Iterator: i=1, j=4 Iterator: i=2, j=3 Iterator: i=3, j=2

Nested for Loop

C# allows a for loop inside another for loop.

Example: Nested for loop

for (int i = 0; i < 2; i++)
{
    for(int j =i; j < 4; j++)
        Console.WriteLine("Value of i: {0}, J: {1} ", i,j);
}

Try it

Output:

Value of i: 0, J: 0 Value of i: 0, J: 1 Value of i: 0, J: 2 Value of i: 0, J: 3 Value of i: 1, J: 1 Value of i: 1, J: 2 Value of i: 1, J: 3