Chapter 2: C# Basics – Variables, Data Types, Operators, Control Flow, and I/O

In this chapter, we dive into the building blocks of C# programming.
You’ll learn how to declare and use variables, understand data types, apply operators, control program flow with conditions and loops, and perform basic input/output operations.

🎯 What You Will Learn

By the end of this chapter, you will:

• Understand variables and data types in C#
• Use operators for arithmetic, comparison, and logic
• Apply control flow statements (if, switch, loops)
• Perform input/output operations with the console
• Practice hands-on exercises to reinforce learning

🧩 Variables and Data Types

What is a Variable?

• A named storage location in memory.
• Holds data that can change during program execution.

Syntax:

int age = 25;
string name = "Irshad";
double salary = 55000.75;

Common Data Types:

Example:

using System;

class Program
{
    static void Main()
    {
        int age = 30;
        string name = "Alice";
        bool isStudent = true;

        Console.WriteLine($"{name} is {age} years old. Student: {isStudent}");
    }
}

👉 Exercise:

• Declare variables for your name, age, and monthly salary.
• Print them in a formatted sentence.

➗ Operators in C#

Arithmetic Operators

int a = 10, b = 3;
Console.WriteLine(a + b); // 13
Console.WriteLine(a - b); // 7
Console.WriteLine(a * b); // 30
Console.WriteLine(a / b); // 3
Console.WriteLine(a % b); // 1

Comparison Operators

Console.WriteLine(a > b);  // true
Console.WriteLine(a == b); // false
Console.WriteLine(a != b); // true

Logical Operators

bool x = true, y = false;
Console.WriteLine(x && y); // false
Console.WriteLine(x || y); // true
Console.WriteLine(!x);     // false

👉 Exercise:

• Write a program to check if a number is even or odd using % operator.
• Write a program to compare two numbers and print the larger one.

🔀 Control Flow

If-Else Statement

int marks = 85;
if (marks >= 90)
    Console.WriteLine("Grade A");
else if (marks >= 75)
    Console.WriteLine("Grade B");
else
    Console.WriteLine("Grade C");

Switch Statement

int day = 3;
switch (day)
{
    case 1: Console.WriteLine("Monday"); break;
    case 2: Console.WriteLine("Tuesday"); break;
    case 3: Console.WriteLine("Wednesday"); break;
    default: Console.WriteLine("Invalid day"); break;
}

Loops

For Loop

for (int i = 1; i <= 5; i++)
{
    Console.WriteLine("Iteration: " + i);
}

While Loop

int count = 1;
while (count <= 5)
{
    Console.WriteLine("Count: " + count);
    count++;
}

Do-While Loop

int num = 1;
do
{
    Console.WriteLine("Number: " + num);
    num++;
} while (num <= 5);

👉 Exercise:

• Write a program to print numbers from 1 to 10 using for.
• Write a program to calculate the sum of numbers from 1 to 100 using while.
• Write a program to display a multiplication table using do-while.

⌨️ Input/Output Basics

Console Output

Console.WriteLine("Hello, World!");
Console.Write("Enter your name: ");

Console Input

string name = Console.ReadLine();
Console.WriteLine("Welcome, " + name);

Parsing Input

Console.Write("Enter your age: ");
int age = int.Parse(Console.ReadLine());
Console.WriteLine("You are " + age + " years old.");

👉 Exercise:

• Write a program to ask the user for two numbers and print their sum.
• Write a program to ask for a name and age, then print:
  "Hello John, you are 25 years old."

📘 Chapter Summary

In this chapter, you learned:

• How to declare and use variables and data types
• How to apply operators for calculations and logic
• How to control program flow with if, switch, and loops
• How to perform basic input/output operations

👉 You also practiced exercises to reinforce learning.