What is and how to use the FOR loop

A for loop is a control structure that repeats a block of code a specified number of times. It is one of the most commonly used control structures in C#.

Basic Syntax

The syntax of a for loop in C# consists of three main parts: initialization, condition, and update. These parts are specified within the parentheses of the for loop and are separated by semicolons.

The basic structure of a for loop in C# is as follows:

for (initialization; condition; update)
{
    // Instructions to execute in each iteration
}

Let’s look at each of the parts:

• Initialization: In this part of the loop, the initial values of the variables that will control the loop’s execution are established (generally, it is used to initialize a counter that will be incremented or decremented in each iteration)

• Condition: The condition is a boolean expression that is evaluated before each iteration. If the condition is true, the instructions inside the loop are executed. If the condition is false, the loop is exited, and the program continues execution.

• Update: In this part of the loop, an action is performed that modifies the value of the variables that control the loop (generally, it is used to increment or decrement the counter)

• Instructions to execute: Here, the instructions that are executed in each iteration are specified. These instructions can be any valid code in C# (such as assignments, calculations, method calls, etc.)

Basic Example

Let’s look at a simple example where a for loop is used to print the numbers from 1 to 10:

for (int i = 1; i <= 10; i++)
{
    Console.WriteLine(i);
}

The result is that the numbers from 1 to 10 will be displayed on the screen.

Modifying the flow of the loop

Skipping iterations with continue

The continue statement is used to skip the current iteration and jump directly to the next iteration of the loop.

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

Breaking the loop with break

Using the break statement allows you to exit the loop before the condition is met. This is useful in situations where a specific value is found, and there is no need to continue iterating.

for (int i = 0; i < 10; i++)
{
    if (i == 5)
    {
        break;
    }
    Console.WriteLine(i);
}

Special Cases

It is possible to create more “original” cases of the for loop. Generally, it is not a good idea to do so. But I mention it, if only so that if you see it someday, you can scold someone. 😉

Using external variables

It is possible to use a variable declared outside the for loop as the control variable. However, this can lead to confusion and errors if not managed properly:

int i = 0;
for (i = 0; i < 5; i++)
{
    Console.WriteLine(i);
}
Console.WriteLine($"Value of i after the loop: {i}");

Multiple declarations

In the initialization and update sections, multiple declarations can be included, separated by commas. This is useful when multiple control variables are needed:

for (int i = 0, j = 10; i < j; i++, j--)
{
    Console.WriteLine($"i: {i}, j: {j}");
}

Practical Examples

int number = 5; // Number for which the multiplication table is generated

for (int i = 1; i <= 10; i++) // Iterates from 1 to 10
{
    Console.WriteLine($"{number} x {i} = {number * i}"); // Prints the multiplication of the number by 'i'
}

int[] numbers = { 1, 2, 3, 4, 5 }; // Declare the array
int sum = 0; // Variable to store the sum

for (int i = 0; i < numbers.Length; i++)
{
    sum += numbers[i]; // Add each element of the array to 'sum'
}

Console.WriteLine($"The sum of the elements is: {sum}");

for (int i = 0; i < 10; i += 2) // Increments 'i' by 2 in each iteration
{
    Console.WriteLine(i); // Prints the current value of 'i'
}

for (int i = 10; i > 0; i--) // Decrements 'i' by 1 in each iteration
{
    Console.WriteLine(i); // Prints the current value of 'i'
}

int[] numbers = { 1, 2, 3, 4, 5 }; // Declare the array
int search = 3; // Number to search for
bool found = false; // Variable to indicate if the number was found

for (int i = 0; i < numbers.Length; i++)
{
    if (numbers[i] == search) // Compares each element with the searched number
    {
        found = true; // Marks that the number was found
        break; // Exits the loop
    }
}

if (found)
{
    Console.WriteLine($"The number {search} is found in the array.");
}
else
{
    Console.WriteLine($"The number {search} is not found in the array.");
}