Conditions & Looping

1. Description

Conditions (like if, else, and switch) let a program choose behavior based on values. Looping constructs (for, while, do-while, foreach) repeat actions until a condition is met. Together, they control the flow of your program.

2. Why It Is Important

Branching and repetition are essential: they let programs react to input, iterate collections, and perform repeated tasks such as processing lists or retrying operations.

3. Real-World Examples

• Validating user input and responding accordingly.
• Iterating over a list of orders to process each one.
• Retrying a network call a fixed number of times.
• Building menu-driven console tools.

4. Syntax & Explanation

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        int score = 85;

        // if / else
        if (score >= 90)
            Console.WriteLine("Grade: A");
        else if (score >= 75)
            Console.WriteLine("Grade: B");
        else
            Console.WriteLine("Grade: C or below");

        // switch
        string command = "start";
        switch (command)
        {
            case "start":
                Console.WriteLine("Started");
                break;
            case "stop":
                Console.WriteLine("Stopped");
                break;
            default:
                Console.WriteLine("Unknown command");
                break;
        }

        // for loop
        for (int i = 0; i < 3; i++)
            Console.WriteLine($"for: {i}");

        // while loop
        int n = 3;
        while (n-- > 0)
            Console.WriteLine($"while: {n}");

        // foreach loop
        var names = new List<string> { "Alice", "Bob", "Charlie" };
        foreach (var name in names)
            Console.WriteLine($"Hello {name}");
    }
}

5. Use Cases

• Looping through collections (files, database rows, API results).
• Implementing retry logic and timeouts.
• Menu handling and state machines in console apps.

6. Mini Practice Task

1. Write a program that prints all even numbers from 1 to 20 using a for loop.
2. Read numbers until the user types 0, then print the sum (use while).