C# Programming Tutorial: From Fundamentals to Advanced Application Development

📘 Chapter 3: Control Flow and Error Handling in C#

🧠 Introduction

A real-world program needs more than just logic—it needs the ability to make decisions, repeat tasks, and handle errors gracefully. This chapter explores control flow statements that allow branching and looping, along with error handling techniques in C#.

🔄 1. Control Flow in C#

Control flow determines how and when different parts of your code get executed. In C#, it includes:

• Conditional Statements (if, else, switch)
• Looping Statements (for, while, do-while, foreach)
• Jump Statements (break, continue, return, goto)

✅ 2. Conditional Statements

🔹 if Statement

Executes code only if a condition is true.

int age = 18;

if (age >= 18)

{

    Console.WriteLine("You are eligible to vote.");

}

🔹 if-else Statement

Provides an alternate block if the condition is false.

if (age < 18)

{

    Console.WriteLine("Not eligible.");

}

else

{

    Console.WriteLine("Eligible.");

}

🔹 else if Ladder

Used for multiple conditions.

int marks = 75;

if (marks >= 90)

    Console.WriteLine("Grade A");

else if (marks >= 75)

    Console.WriteLine("Grade B");

else

    Console.WriteLine("Grade C");

🔹 switch Statement

Efficient for multiple discrete values.

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;

}

📋 Comparison Table – Conditionals

🔁 3. Looping Statements

Used for repeating code blocks.

🔹 for Loop

Used when the number of iterations is known.

for (int i = 0; i < 5; i++)

{

    Console.WriteLine(i);

}

🔹 while Loop

Executes while a condition is true.

int i = 0;

while (i < 5)

{

    Console.WriteLine(i);

    i++;

}

🔹 do-while Loop

Always executes at least once.

int j = 0;

do

{

    Console.WriteLine(j);

    j++;

} while (j < 5);

🔹 foreach Loop

Iterates over collections.

string[] colors = { "Red", "Green", "Blue" };

foreach (string color in colors)

{

    Console.WriteLine(color);

}

📋 Comparison Table – Loops

🚀 4. Jump Statements

🔹 break

Exits a loop or switch.

for (int i = 1; i <= 5; i++)

{

    if (i == 3)

        break;

    Console.WriteLine(i); // 1 2

}

🔹 continue

Skips to next iteration.

for (int i = 1; i <= 5; i++)

{

    if (i == 3)

        continue;

    Console.WriteLine(i); // 1 2 4 5

}

🔹 return

Exits the method and optionally returns a value.

int GetNumber()

{

    return 42;

}

🔹 goto (use with caution)

Used to jump to a labeled statement.

int i = 0;

start:

if (i < 3)

{

    Console.WriteLine(i++);

    goto start;

}

⚠️ 5. Error Handling in C#

Errors are inevitable. Without proper handling, they can crash your program. C# provides structured exception handling using:

• try
• catch
• finally
• throw

✅ try-catch Block

try

{

    int x = 5, y = 0;

    Console.WriteLine(x / y); // Division by zero!

}

catch (DivideByZeroException e)

{

    Console.WriteLine("Error: " + e.Message);

}

✅ Multiple catch Blocks

try

{

    int[] arr = { 1, 2 };

    Console.WriteLine(arr[5]);

}

catch (IndexOutOfRangeException e)

{

    Console.WriteLine("Index out of range");

}

catch (Exception ex)

{

    Console.WriteLine("General error");

}

✅ finally Block

Executes regardless of exception.

try

{

    Console.WriteLine("Try block");

}

finally

{

    Console.WriteLine("Always runs");

}

✅ throw Statement

Used to manually raise exceptions.

throw new InvalidOperationException("Invalid operation");

📦 Common Exception Types in C#

🧪 Sample Program: Error Handling Example

using System;

class Program

{

    static void Main()

    {

        try

        {

            Console.Write("Enter a number: ");

            int num = Convert.ToInt32(Console.ReadLine());

            Console.WriteLine("Reciprocal: " + (1.0 / num));

        }

        catch (DivideByZeroException)

        {

            Console.WriteLine("Cannot divide by zero.");

        }

        catch (FormatException)

        {

            Console.WriteLine("Invalid input.");

        }

        finally

        {

            Console.WriteLine("Execution completed.");

        }

    }

}

🧠 Best Practices for Control Flow and Error Handling

• Avoid deeply nested if statements—use switch or early returns.
• Handle only specific exceptions, not Exception base class unless necessary.
• Always close file/database connections in finally or use using.
• Never use goto unless there’s a very clear use case.

📋 Summary Table