The Power of C#: From Basic Data Types to Advanced Control Flow

Learn how to use arrays, operators, and loops to solve real-world problems in C#.

7 min readJan 27, 2025

C# (pronounced C-Sharp) is a modern, object-oriented programming language developed by Microsoft in the early 2000s. It is part of the .NET ecosystem and is widely used for building various types of applications, including web, desktop, mobile, and cloud-based solutions.

1. Key Features of C#

Object-Oriented: Supports principles like encapsulation, inheritance, and polymorphism.
Strongly Typed: Enforces strict type checking to prevent errors.
Garbage Collection: Automatically manages memory to reduce memory leaks.
Cross-Platform Development: Supports Windows, macOS, and Linux through .NET Core/.NET 5+.
Interoperability: Can work with other languages, including C++ and F#.
Asynchronous Programming: Uses async and await for non-blocking operations.
Secure and Scalable: Provides features like exception handling and access modifiers.

2. Common Uses of C#

Desktop Applications: Using Windows Forms (WinForms) and Windows Presentation Foundation (WPF).
Web Development: With ASP.NET Core for creating web applications and APIs.
Mobile Apps: Using Xamarin or .NET MAUI to build cross-platform applications.
Game Development: With Unity Engine, one of the most popular game development platforms.
Cloud & Enterprise Applications: Through Azure and microservices architectures.

3. Basic C# Example

Here’s a simple “Hello, World!” program in C#

using System;

class Program
{
  static void Main()
  {
    Console.WriteLine("Hello, World!");
  }
}

4. Standard Input and Output

C# provides various ways to handle standard input (stdin) and standard output (stdout) using the System.Console class.

Standard Output

Console.Write() : Prints text without moving to the next line.
Console.WriteLine() : Prints text and moves to the next line.

using System;

class Program
{
  static void Main()
  {
    Console.WriteLine("Hello, World!"); // Prints with a newline
    Console.Write("Enter your name: "); // Prints without a newline
  }
}

Standard Input

Console.ReadLine() reads a full line as a string.

using System;

class Program
{
  static void Main()
  {
    Console.Write("Enter your name: ");
    string name = Console.ReadLine(); // Reads the entire line
    Console.WriteLine("Hello, " + name + "!");
  }
}

If you need to read numbers, you must convert them.

int age = int.Parse(Console.ReadLine());

// Alternative
int age = Convert.ToInt32(Console.ReadLine());

Reading a Single Character

Console.Read() reads a single character as an int (ASCII value).

char character = (char) Console.Read();
Console.WriteLine("Character: " + character);

Formatting Output

C# allows formatted printing using placeholders {}.

using System;

class Program
{
  static void Main()
  {
    string name = "Alice";
    int age = 25;

    Console.WriteLine("Name: {0}, Age: {1}", name, age);

    // Using string interpolation
    Console.WriteLine($"Name: {name}, Age: {age}"); 
  }
}

5. Data Types

C# has two main categories of data types

Value Types : Stored directly in memory.
Reference Types : Store references (memory addresses) to the actual data.

Value Types

Store actual values.
Stored in the stack memory.
When assigned to another variable, a copy of the value is made.
Examples: int, float, char, bool, struct, enum.

int num1 = 10;
int num2 = num1; // num2 gets a COPY of num1's value
num1 = 20; // Changes num1, but num2 remains 10

Console.WriteLine(num1); // Output: 20
Console.WriteLine(num2); // Output: 10

Reference Types

Store a reference (memory address) instead of the actual value.
Stored in the heap memory.
When assigned to another variable, both variables point to the same memory location.
Examples: class, string, object, array, interface, delegate.

class Person
{
  public string Name;
}

Person p1 = new Person();
p1.Name = "John";

Person p2 = p1; // p2 points to the same object in heap memory
p2.Name = "Alice"; // Changing p2 also changes p1

Console.WriteLine(p1.Name); // Output: Alice
Console.WriteLine(p2.Name); // Output: Alice

6. Boxing and Unboxing

Boxing and unboxing are mechanisms that allow conversion between value types and reference types in C#. They are used when storing value types in objects or extracting them back.

Boxing (Value Type → Object)

Converting a value type (int, double, char, etc.) into an object (reference type).
The value type (stack) is moved to the heap inside an object.
Involves memory allocation and copying, making it slower than direct value type operations.

int num = 10; // Value type (stored in stack)
object obj = num; // Boxing: num is wrapped inside an object (stored in heap)

Console.WriteLine(obj); // Output: 10

num is an int (value type).
obj stores num as an object (reference type).

Unboxing (Object → Value Type)

Extracting a value type from an object (reference type).
The value is retrieved from the heap and copied back to the stack.
Can cause exceptions if the cast is incorrect.

object obj = 10; // Boxing
int num = (int) obj; // Unboxing: Extracting int from object

Console.WriteLine(num); // Output: 10

The object obj holds an int (10).
num = (int)obj; converts the object back to an int.

7. Operators

Operators in C# are symbols used to perform operations on variables and values. C# provides various types of operators.

Arithmetic Operators

Function: Perform mathematical operations.
Symbols: +, -, *, /, %
Example: a + b, a * b

Assignment Operators

Function: Assign values to variables.
Symbols: =, +=, -=, *=, /=, %=, &=, |=, ^=, <<=, >>=
Example: x += 5 (Equivalent to x = x + 5)

Comparison (Relational) Operators

Function: Compare values and return true or false.
Symbols: ==, !=, >, <, >=, <=
Example: a > b, x == y

Logical Operators

Function: Perform logical operations and return true or false.
Symbols: &&, ||, !
Example: (a > b) && (c < d)

Bitwise Operators

Function: Perform bit-level operations on integer values.
Symbols: &, |, ^, ~, <<, >>
Example: a & b, a << 2

Increment & Decrement Operators

Function: Increase or decrease the value of a variable.
Symbols: ++, --
Example: ++x, x--

Ternary Operator

Function: Shorten if-else statements.
Symbol: ? :
Example: result = (a > b) ? "A is greater" : "B is greater";

Null-Coalescing Operators

Function: Handle null values safely.
Symbols: ??
Example: name = userName ?? "Guest";

Type Cast Operators

Function: Convert between different data types.
Symbols: (type)
Example: int num = (int)doubleValue;

8. Decision-Making

Decision-making structures allow a program to execute different code blocks based on conditions. C# provides the following decision-making statements.

`if` Statement

Executes a block of code if a condition is true.

int num = 10;
if (num > 5)
{
  Console.WriteLine("Number is greater than 5");
}

`if-else` Statement

Executes one block if the condition is true, otherwise executes another block.

int age = 18;
if (age >= 18)
{
  Console.WriteLine("Eligible to vote");
}
else
{
  Console.WriteLine("Not eligible to vote");
}

`if-else if-else` Statement

Checks multiple conditions sequentially.

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

Used when multiple possible values need to be checked for a variable.

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;
}

`switch` Expression (C# 8.0 and later)

A modern way to write switch statements more concisely.

int num = 2;
string result = num switch
{
  1 => "One",
  2 => "Two",
  3 => "Three",
  _ => "Unknown Number"
};
Console.WriteLine(result);

9. Loops

Loops allow you to execute a block of code multiple times, depending on a condition. C# provides several types of loops to handle different situations.

`for` Loop

The for loop is used when the number of iterations is known beforehand.

for (int i = 0; i < 5; i++)
{
  Console.WriteLine(i);
}

`while` Loop

The while loop is used when you want to repeat a block of code as long as the condition is true. The condition is evaluated before the execution.

int i = 0;
while (i < 5)
{
  Console.WriteLine(i);
  i++;
}

`do..while` Loop

The do..while loop guarantees that the code block is executed at least once, even if the condition is false. The condition is checked after each iteration.

int i = 0;
do
{
  Console.WriteLine(i);
  i++;
} while (i < 5);

`foreach` Loop

The foreach loop is used to iterate over a collection (like arrays, lists, etc.). It simplifies iterating through collections without needing to manage an index.

int[] numbers = { 1, 2, 3, 4, 5 };
foreach (int number in numbers)
{
  Console.WriteLine(number);
}

10. Arrays

An array is a collection of elements of the same data type stored in contiguous memory locations. C# provides different types of arrays.

One-Dimensional Array

A simple list-like structure where elements are stored in a single row.

int[] numbers = new int[5]; // Declare an array of size 5
numbers[0] = 10;            // Assign values
numbers[1] = 20;

int[] arr = { 10, 20, 30, 40, 50 }; // Declare & initialize
foreach (int num in arr)
{
  Console.WriteLine(num);
}

Multi-Dimensional (Rectangular) Array

A rectangular array has fixed rows and columns like a matrix. All rows have the same number of columns.

int[,] matrix = new int[2, 3]; // 2 rows, 3 columns
matrix[0, 0] = 1;
matrix[1, 2] = 5;

int[,] matrix = { { 1, 2, 3 }, { 4, 5, 6 } }; // Declare & initialize
for (int i = 0; i < 2; i++)
{
  for (int j = 0; j < 3; j++)
  {
    Console.Write(matrix[i, j] + " ");
  }
  Console.WriteLine();
}

Jagged Array

A jagged array is an array of arrays, where each row can have different lengths.

int[][] jagged = new int[3][]; // Declare with 3 rows
jagged[0] = new int[] { 1, 2, 3 };
jagged[1] = new int[] { 4, 5 };
jagged[2] = new int[] { 6, 7, 8, 9 };

int[][] jaggedArray =
{
  new int[] { 1, 2, 3 },
  new int[] { 4, 5 },
  new int[] { 6, 7, 8, 9 }
};

for (int i = 0; i < jaggedArray.Length; i++)
{
  foreach (int num in jaggedArray[i])
  {
    Console.Write(num + " ");
  }
  Console.WriteLine();
}

Practical Questions

Write a program that takes an array of integers and finds the largest number in the array.
Create a program that takes an array of integers and calculates the average of all the numbers in the array.
Create a program that takes a list of integers and prints out the smallest even number in the array.
Write a program that accepts an array of integers and prints all the prime numbers in the array.
Write a program that counts how many times a specific number appears in an array.
Write a program that checks if an array of integers forms a palindrome (i.e., the array reads the same backward and forward).
Write a program that checks if one array is a subset of another array.