Lesson 7: Loops (for, while, do-while) in C#

Welcome to Lesson 7! In this lesson, we’ll explore loops in C#, which are fundamental for repeating code blocks multiple times. Loops help you handle repetitive tasks efficiently and are essential for many programming tasks. We’ll cover three types of loops in C#: for, while, and do-while.

1. The for Loop

The for loop is used when you know in advance how many times you want to execute a block of code. It consists of three parts: initialization, condition, and iteration.

Syntax:

for (initialization; condition; iteration)
{
    // Code to execute each time the loop runs
}

Example:

for (int i = 0; i < 5; i++)
{
    Console.WriteLine("Iteration: " + i);
}

Explanation:

• Initialization: int i = 0 sets up the loop variable i to start at 0.
• Condition: i < 5 specifies that the loop should continue as long as i is less than 5.
• Iteration: i++ increments i by 1 after each loop iteration.
• The code inside the loop prints the value of i each time the loop runs.

2. The while Loop

The while loop is used when you want to repeat a block of code as long as a specified condition is true. It’s suitable when you don’t know in advance how many times the loop will need to run.

Syntax:

while (condition)
{
    // Code to execute as long as the condition is true
}

Example:

int j = 0;

while (j < 5)
{
    Console.WriteLine("Iteration: " + j);
    j++;
}

Explanation:

• The loop continues as long as j is less than 5.
• The code inside the loop prints the value of j and then increments j by 1.

3. The do-while Loop

The do-while loop is similar to the while loop, but it guarantees that the loop’s code block is executed at least once, even if the condition is false initially.

Syntax:

do
{
    // Code to execute at least once, and then repeat while the condition is true
}
while (condition);

Example:

int k = 0;

do
{
    Console.WriteLine("Iteration: " + k);
    k++;
}
while (k < 5);

Explanation:

• The do block executes first before checking the condition.
• The loop continues to run as long as k is less than 5.

4. Nested Loops

You can nest loops within other loops to handle more complex scenarios, such as iterating through multi-dimensional data.

Example:

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

Explanation:

• The outer for loop runs 3 times.
• For each iteration of the outer loop, the inner for loop runs 3 times.
• This results in a total of 9 iterations, printing all combinations of i and j.

5. Using break and continue

• break: Exits the loop immediately, regardless of the loop condition.
• continue: Skips the current iteration and proceeds to the next iteration of the loop.

Example:

for (int i = 0; i < 10; i++)
{
    if (i == 5)
    {
        break; // Exit the loop when i equals 5
    }
    Console.WriteLine("i: " + i);
}

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

Explanation:

• In the first for loop, break exits the loop when i equals 5, so only values from 0 to 4 are printed.
• In the second for loop, continue skips even numbers, printing only odd values from 1 to 9.

6. Example: Looping Through an Array

Loops are often used to iterate through arrays and collections.

Example:

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

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

Explanation:

• The for loop iterates over each element of the fruits array and prints it.

7. Example: Sum of Numbers

Let’s use a while loop to calculate the sum of numbers from 1 to 10.

Example:

int sum = 0;
int number = 1;

while (number <= 10)
{
    sum += number;
    number++;
}

Console.WriteLine("Sum of numbers from 1 to 10: " + sum);

Explanation:

• The while loop adds numbers from 1 to 10 to the sum variable.
• After the loop completes, it prints the total sum.

Summary

In this lesson, you learned about the three main types of loops in C#: for, while, and do-while. We covered their syntax, use cases, and how to use them to handle repetitive tasks in your code. Additionally, we explored nested loops, and the break and continue statements to control loop execution more precisely.

Happy coding!