This section introduces the fundamental building blocks of C#. Understanding these basics is crucial before diving into more advanced topics.

1. Basic Syntax of C#

A typical C# program consists of:

• Namespace declaration: A way to group related classes.

• Class declaration: Defines the blueprint of an object.

• Main method: Entry point where execution begins.

• Statements and Expressions: Instructions executed line by line.

Example: Basic Structure

using System; // Namespace declaration

class Program // Class declaration
{
    static void Main() // Main method
    {
        Console.WriteLine("Hello, World!"); // Statement
    }
}

Explanation:

1. using System: Includes the System namespace to use built-in functionality like Console.

2. class Program: Defines a class named Program. All code resides within classes in C#.

3. static void Main(): The main method where program execution starts.

4. Statements end with a semicolon (;).

5. Curly braces {} define blocks of code.

 

2. Data Types in C#

• In C#, data types are divided into two main categories:

• Value Types:

  • Store data directly in their own memory space.

  • Examples: int, float, char, bool, struct, and enums.

  • Operations on a value type create a copy of the value.

• Reference Types:

  • Store references (memory addresses) that point to the actual data.

  • Examples: string, object, arrays, and classes.

  • Operations on a reference type affect the original data because they share the same memory location.

 

Common Data Types

Type	Size	Description	Example
int	4 bytes	Whole numbers	int num = 10;
double	8 bytes	Decimal numbers	double pi = 3.14;
char	2 bytes	Single character	char initial = 'A';
string	Variable	Sequence of characters	string name = "Tom";
bool	1 byte	True or false	bool isActive = true;

 

Example: Difference Between Value and Reference Types

using System;

class Program
{
    static void Main()
    {
        // Example of a Value Type
        int valueType1 = 10;
        int valueType2 = valueType1; // Copy of the value is created
        valueType2 = 20; // Changing valueType2 does not affect valueType1

        Console.WriteLine("ValueType1: " + valueType1); // Output: 10
        Console.WriteLine("ValueType2: " + valueType2); // Output: 20

        // Example of a Reference Type
        string[] referenceType1 = { "A", "B", "C" };
        string[] referenceType2 = referenceType1; // Both point to the same memory location
        referenceType2[0] = "Z"; // Changing referenceType2 affects referenceType1

        Console.WriteLine("ReferenceType1[0]: " + referenceType1[0]); // Output: Z
        Console.WriteLine("ReferenceType2[0]: " + referenceType2[0]); // Output: Z
    }
}

Key Points

• Value Types: Stored in the stack, changes do not affect other variables.

• Reference Types: Stored in the heap, changes are reflected across all references pointing to the same object.

 

3. Operators in C#

Categories of Operators

1. Arithmetic Operators: Perform basic calculations.

   • Examples: +, -, *, /, %

2. Comparison Operators: Compare two values.

   • Examples: ==, !=, >, <, >=, <=

3. Logical Operators: Combine multiple conditions.

   • Examples: &&, ||, !

Example: Using Operators

int a = 10, b = 3;

// Arithmetic
Console.WriteLine(a + b); // Output: 13

// Comparison
Console.WriteLine(a > b); // Output: True

// Logical
Console.WriteLine(a > b && b > 0); // Output: True

 

4. Input and Output

Input from User

• Use Console.ReadLine() to read input as a string.

Example: User Input

//input from user
Console.Write("Enter your name: ");
string name = Console.ReadLine(); 

//output
Console.WriteLine("Hello, " + name);

Output to Console

• Use Console.WriteLine() to print messages or data.

Example: Output

int age = 25; 
Console.WriteLine("Your age is: " + age);

 

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Practice Exercises

1. Write a program that calculates the area of a rectangle. Take length and width as inputs.

2. Create a program that checks if a number is even or odd.

3. Build a simple calculator that performs addition, subtraction, multiplication, and division based on user input.