Conditional Statements in C#

# CHAPTER 7

Conditional Statements #

1. Introduction #

2. Learning Objectives #

• Use the if statement to execute code conditionally.

• Use if-else for two-way branching.

• Chain conditions using else if ladders.

• Use the switch statement for multi-way branching.

• Use modern C# 8.0 switch expressions (Pattern Matching).

3. The if and else Statements #

int age = 20;

if (age >= 18) 
{
    Console.WriteLine("You are an adult.");
} 
else 
{
    Console.WriteLine("You are a minor.");
}

4. The else if Ladder #

int score = 75;

if (score >= 90) 
{
    Console.WriteLine("Grade: A");
} 
else if (score >= 80) 
{
    Console.WriteLine("Grade: B");
} 
else if (score >= 70) 
{
    Console.WriteLine("Grade: C");
} 
else 
{
    Console.WriteLine("Grade: F");
}
// Output: Grade: C

5. The switch Statement #

int day = 3;

switch (day) 
{
    case 1:
        Console.WriteLine("Monday");
        break; // break is REQUIRED in C# to exit the switch
    case 2:
        Console.WriteLine("Tuesday");
        break;
    case 3:
        Console.WriteLine("Wednesday");
        break;
    default: // Runs if no cases match
        Console.WriteLine("Weekend!");
        break;
}

Important Difference from C/C++: In C#, you cannot "fall through" from one case to another by forgetting the break keyword. The C# compiler will throw an error to protect you from this common bug!

6. Modern C# (Switch Expressions / Pattern Matching) #

int day = 3;

// Modern C# Switch Expression
string dayName = day switch
{
    1 => "Monday",
    2 => "Tuesday",
    3 => "Wednesday",
    _ => "Weekend" // The underscore '_' represents the 'default' case
};

Console.WriteLine(dayName);

7. Mini Project: Grade Evaluation System #

using System;

namespace GradeCalculator
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("=== GRADE EVALUATOR ===");
            Console.Write("Enter your score (0-100): ");
            int score = int.Parse(Console.ReadLine());

            if (score < 0 || score > 100) 
            {
                Console.WriteLine("Error: Invalid score entered.");
            } 
            else if (score >= 90) 
            {
                Console.WriteLine("Result: A (Excellent)");
            } 
            else if (score >= 80) 
            {
                Console.WriteLine("Result: B (Good)");
            } 
            else if (score >= 70) 
            {
                Console.WriteLine("Result: C (Pass)");
            } 
            else 
            {
                Console.WriteLine("Result: F (Fail)");
            }
        }
    }
}

8. Common Mistakes #

• Using = instead of ==: Writing if (x = 5) assigns 5 to x. The C# compiler is smart and will flag this as an error (unlike C++ which allows it and causes massive bugs).

• Missing break in a traditional switch: C# strictly enforces that every case block (that contains code) must end with a break or return.

9. Best Practices #

• Keep your if statements simple. If an if statement has 4 && and || conditions, refactor it by extracting those conditions into well-named boolean variables.

• Use the modern C# 8 switch expression when mapping a single variable to a single return value. It is much cleaner than a traditional switch.

10. Exercises #

1. 1. Write a program to check if a given year (input by user) is a leap year.

1. 2. Build a simple calculator using a switch statement that asks the user for an operator (+, -, *, /) and two numbers.

11. MCQs with Answers #

12. Interview Questions #

• Q: Explain the difference between a traditional switch statement and a modern C# switch expression.

• Q: Why does C# prohibit implicit fall-through in switch cases? (Answer: To prevent accidental bugs caused by forgotten break statements, a notorious issue in C/C++).

13. Summary #

14. Next Chapter Recommendation #