C# for Loop

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.

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.

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

In the above example, int i = 0 is an initializer where we define an int variable i and initialize it with 0. The second section is the condition expression i < 10, if this condition returns true then it will execute a code block. After executing the code block, it will go to the third section, iterator. The i++ is an incremental statement that increases the value of a loop variable i by 1. Now, it will check the conditional expression again and repeat the same thing until conditional expression returns false. The below figure illustrates the execution steps of the for loop.

The below figure illustrates the execution steps of the for loop.

If a code block only contains a single statement, then you don't need to wrap it inside curly brackets { }, as shown below.

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

An Initializer, condition, and iterator sections are optional. You can initialize a variable before for loop, and condition and iterator can be defined inside a code block, as shown below.

int i = 0;

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

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.

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

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

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

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

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

Exit the for Loop

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

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

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

Multiple Expressions

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

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

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

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

Nested for Loop

C# allows a for loop inside another 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);
}