C# Loops

Loops are fundamental constructs in C# that allow developers to execute a block of code repeatedly based on certain conditions. They are essential for tasks such as iterating over collections, processing data, and automating repetitive tasks. Understanding the different types of loops and their appropriate use cases is crucial for writing efficient and maintainable code.

1. Overview of Loops

2. The `for` Loop

for (initialization; condition; iteration)
{
    // Code to execute
}

using System;

class Program
{
    static void Main()
    {
        for (int i = 1; i <= 5; i++)
        {
            Console.WriteLine($"Iteration {i}");
        }
    }
}

Output:
Iteration 1
Iteration 2
Iteration 3
Iteration 4
Iteration 5

3. The `foreach` Loop

foreach (var item in collection)
{
    // Code to execute for each item
}

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List<string> fruits = new List<string> { "Apple", "Banana", "Cherry" };

        foreach (string fruit in fruits)
        {
            Console.WriteLine($"Fruit: {fruit}");
        }
    }
}

Output:
Fruit: Apple
Fruit: Banana
Fruit: Cherry

4. The `while` Loop

while (condition)
{
    // Code to execute
}

using System;

class Program
{
    static void Main()
    {
        int count = 1;

        while (count <= 3)
        {
            Console.WriteLine($"Count: {count}");
            count++;
        }
    }
}

Output:
Count: 1
Count: 2
Count: 3

5. The `do-while` Loop

do
{
    // Code to execute
} while (condition);

using System;

class Program
{
    static void Main()
    {
        int number = 5;

        do
        {
            Console.WriteLine($"Number is {number}");
            number++;
        } while (number < 5);
    }
}

Output:
Number is 5

6. Nested Loops

using System;

class Program
{
    static void Main()
    {
        for (int i = 1; i <= 3; i++)
        {
            for (int j = 1; j <= 2; j++)
            {
                Console.WriteLine($"Outer Loop {i}, Inner Loop {j}");
            }
        }
    }
}

Output:
Outer Loop 1, Inner Loop 1
Outer Loop 1, Inner Loop 2
Outer Loop 2, Inner Loop 1
Outer Loop 2, Inner Loop 2
Outer Loop 3, Inner Loop 1
Outer Loop 3, Inner Loop 2

7. Control Statements within Loops

using System;

class Program
{
    static void Main()
    {
        for (int i = 1; i <= 5; i++)
        {
            if (i == 3)
                break;
            Console.WriteLine($"i = {i}");
        }
    }
}

Output:
i = 1
i = 2

using System;

class Program
{
    static void Main()
    {
        for (int i = 1; i <= 5; i++)
        {
            if (i == 3)
                continue;
            Console.WriteLine($"i = {i}");
        }
    }
}

Output:
i = 1
i = 2
i = 4
i = 5

using System;

class Program
{
    static void Main()
    {
        for (int i = 1; i <= 5; i++)
        {
            if (i == 3)
                goto EndLoop;
            Console.WriteLine($"i = {i}");
        }

        EndLoop:
        Console.WriteLine("Loop terminated.");
    }
}

Output:
i = 1
i = 2
Loop terminated.

8. Infinite Loops

using System;

class Program
{
    static void Main()
    {
        while (true)
        {
            Console.WriteLine("This loop will run forever.");
            // Use break conditionally to exit
            break; // Removing this will cause an infinite loop
        }
    }
}

Output:
This loop will run forever.

9. Looping Constructs in Modern C#

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        List<int> numbers = new List<int> { 1, 2, 3, 4, 5 };
        var evenNumbers = numbers.Where(n => n % 2 == 0);

        foreach (var num in evenNumbers)
        {
            Console.WriteLine($"Even Number: {num}");
        }
    }
}

Output:
Even Number: 2
Even Number: 4

10. Best Practices for Using Loops

11. Common Mistakes and How to Avoid Them

for (int i = 0; i <= 10; i++) // Should be i < 10 for 0-9
{
  Console.WriteLine(i);
}

12. Real-World Example: Processing User Input

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List<string> userInputs = new List<string> { "Alice", "Bob", "", "Charlie", null, "Dave" };

        foreach (var input in userInputs)
        {
            if (string.IsNullOrWhiteSpace(input))
            {
                Console.WriteLine("Invalid input detected. Skipping...");
                continue;
            }

            Console.WriteLine($"Processing user: {input}");
        }

        // Using a for loop to count valid inputs
        int validCount = 0;
        for (int i = 0; i < userInputs.Count; i++)
        {
            if (!string.IsNullOrWhiteSpace(userInputs[i]))
            {
                validCount++;
            }
        }
        Console.WriteLine($"Total valid inputs: {validCount}");
    }
}

Output:
Processing user: Alice
Processing user: Bob
Invalid input detected. Skipping...
Processing user: Charlie
Invalid input detected. Skipping...
Processing user: Dave
Total valid inputs: 4

13. Advanced Topics

using System;
using System.Threading.Tasks;

class Program
{
  static void Main()
  {
      Parallel.For(0, 5, i =>
      {
          Console.WriteLine($"Parallel iteration {i} on thread {System.Threading.Thread.CurrentThread.ManagedThreadId}");
      });
  }
}

Output:
(Order may vary due to parallel execution) Parallel iteration 0 on thread 4
Parallel iteration 1 on thread 5
Parallel iteration 2 on thread 6
Parallel iteration 3 on thread 4
Parallel iteration 4 on thread 5

using System;
using System.Collections.Generic;

class Program
{
  static void Main()
  {
      foreach (var number in GetNumbers(3))
      {
          Console.WriteLine($"Number: {number}");
      }
  }

  static IEnumerable<int> GetNumbers(int count)
  {
      for (int i = 1; i <= count; i++)
      {
          yield return i;
      }
  }
}

Output:
Number: 1
Number: 2
Number: 3

14. Summary

Key points