🚦 Program Flow: Control Flow in C#

The Traffic Controller Inside Your Code

Imagine you’re a traffic controller at a busy intersection. Cars are coming from all directions, and YOUR job is to decide:

• Which cars go now?
• Which cars wait?
• Which cars go around in circles until something happens?

That’s EXACTLY what Control Flow does in C#! It’s the traffic controller that tells your code which path to take.

🎯 What You’ll Master

graph TD
    A[Control Flow] --> B[If-Else]
    A --> C[Switch]
    A --> D[Loops]
    A --> E[Loop Control]
    B --> B1[Make Decisions]
    C --> C1[Choose One Path]
    D --> D1[Repeat Actions]
    E --> E1[Control Repetition]

🔀 If-Else Statements

The “Yes or No” Decision Maker

Think of if-else like asking a simple question: “Is this true?”

If YES → Do this thing If NO → Do that other thing

The Basic Pattern

int age = 10;

if (age >= 18)
{
    Console.WriteLine("You can vote!");
}
else
{
    Console.WriteLine("Too young to vote.");
}

Output: Too young to vote.

Because 10 is NOT greater than or equal to 18, we go to the else path!

🎂 Real Life Example: Birthday Cake

int cakeSlices = 3;
int guests = 5;

if (cakeSlices >= guests)
{
    Console.WriteLine("Everyone gets cake!");
}
else
{
    Console.WriteLine("We need more cake!");
}

Output: We need more cake!

3 slices for 5 guests? Not enough!

🪜 What If There Are MORE Options? (Else-If)

Sometimes it’s not just yes/no. It’s multiple choices!

Think of a slide at the playground:

• Too short? → Can’t go on the big slide
• Just right? → Use the medium slide
• Tall enough? → Use the big slide!

int height = 120; // centimeters

if (height < 100)
{
    Console.WriteLine("Small slide for you!");
}
else if (height < 140)
{
    Console.WriteLine("Medium slide - perfect!");
}
else
{
    Console.WriteLine("Big slide! Wheee!");
}

Output: Medium slide - perfect!

The code checks top to bottom. First true condition wins!

🧩 Nested If: Decisions Inside Decisions

Sometimes you need to ask MORE questions after the first one.

bool hasTicket = true;
int age = 8;

if (hasTicket)
{
    if (age >= 10)
    {
        Console.WriteLine("Enjoy the roller coaster!");
    }
    else
    {
        Console.WriteLine("Try the kids' ride!");
    }
}
else
{
    Console.WriteLine("Buy a ticket first!");
}

Output: Try the kids' ride!

First we check the ticket. THEN we check the age!

🎚️ Switch Statements

The Multiple Choice Champion

Imagine a vending machine. You press:

• Button 1 → Chips
• Button 2 → Candy
• Button 3 → Soda
• Button 4 → Cookie

That’s a switch statement! One input, multiple possible outputs.

The Basic Pattern

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("Another day");
        break;
}

Output: Wednesday

The break is super important! It says “STOP here, don’t keep going!”

🍕 Pizza Topping Example

string choice = "B";

switch (choice)
{
    case "A":
        Console.WriteLine("Pepperoni Pizza!");
        break;
    case "B":
        Console.WriteLine("Cheese Pizza!");
        break;
    case "C":
        Console.WriteLine("Veggie Pizza!");
        break;
    default:
        Console.WriteLine("Invalid choice!");
        break;
}

Output: Cheese Pizza!

🎨 Multiple Cases, Same Result

What if pressing 1 OR 2 should do the same thing?

char grade = 'A';

switch (grade)
{
    case 'A':
    case 'B':
        Console.WriteLine("Great job!");
        break;
    case 'C':
        Console.WriteLine("Good effort!");
        break;
    case 'D':
    case 'F':
        Console.WriteLine("Keep trying!");
        break;
    default:
        Console.WriteLine("Unknown grade");
        break;
}

Output: Great job!

Both ‘A’ and ‘B’ fall into the same action!

🔄 Loops

The “Do It Again” Machines

Imagine you’re bouncing a ball. You don’t just bounce ONCE. You bounce again and again and again!

Loops let your code repeat actions without writing the same thing 100 times.

🔢 For Loop: “Do This EXACTLY N Times”

Use for when you KNOW how many times to repeat.

The Basic Pattern

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

Output:

Bounce 1
Bounce 2
Bounce 3
Bounce 4
Bounce 5

Breaking It Down:

graph TD
    A["int i = 1"] --> B["i <= 5 ?"]
    B -->|YES| C["Run the code"]
    C --> D["i++"]
    D --> B
    B -->|NO| E["EXIT loop"]

🌟 Star Pattern Example

for (int i = 1; i <= 4; i++)
{
    for (int j = 1; j <= i; j++)
    {
        Console.Write("*");
    }
    Console.WriteLine();
}

Output:

*
**
***
****

Nested loops = loops inside loops!

🔁 While Loop: “Keep Going UNTIL…”

Use while when you DON’T know exactly how many times.

Think of it like: “Keep eating cookies UNTIL the jar is empty.”

int cookies = 5;

while (cookies > 0)
{
    Console.WriteLine("Yum! Cookies left: " + cookies);
    cookies--;
}
Console.WriteLine("No more cookies!");

Output:

Yum! Cookies left: 5
Yum! Cookies left: 4
Yum! Cookies left: 3
Yum! Cookies left: 2
Yum! Cookies left: 1
No more cookies!

⚠️ Careful: Infinite Loop!

// DON'T DO THIS!
while (true)
{
    Console.WriteLine("Forever...");
}

This runs FOREVER and crashes your program!

Always make sure your loop can end!

🎯 Do-While Loop: “Do Once, Then Check”

The do-while loop ALWAYS runs at least ONCE.

It’s like: “Jump in the pool FIRST, then check if the water is cold.”

int number;
do
{
    Console.WriteLine("Enter a positive number:");
    number = int.Parse(Console.ReadLine());
} while (number <= 0);

Console.WriteLine("You entered: " + number);

Even if the user enters a positive number immediately, the code runs once!

While vs Do-While

📦 Foreach Loop: “For Each Item In…”

Perfect for going through a collection of items!

string[] fruits = {"Apple", "Banana", "Cherry"};

foreach (string fruit in fruits)
{
    Console.WriteLine("I love " + fruit);
}

Output:

I love Apple
I love Banana
I love Cherry

No counting needed! It automatically visits EACH item.

🎮 Loop Control Statements

The Emergency Buttons

Sometimes you need to stop early or skip ahead!

🛑 Break: “STOP! Exit Now!”

break immediately exits the loop. Game over!

for (int i = 1; i <= 10; i++)
{
    if (i == 5)
    {
        Console.WriteLine("Found it! Stopping.");
        break;
    }
    Console.WriteLine("Searching... " + i);
}

Output:

Searching... 1
Searching... 2
Searching... 3
Searching... 4
Found it! Stopping.

We never reach 6, 7, 8, 9, 10!

⏭️ Continue: “Skip This One!”

continue skips the current round and jumps to the next.

for (int i = 1; i <= 5; i++)
{
    if (i == 3)
    {
        continue; // Skip number 3
    }
    Console.WriteLine("Number: " + i);
}

Output:

Number: 1
Number: 2
Number: 4
Number: 5

Number 3 is SKIPPED!

🏷️ Break vs Continue

graph LR
    A[Loop Running] --> B{Special Case?}
    B -->|break| C[EXIT Loop Completely]
    B -->|continue| D[Skip to Next Round]
    B -->|neither| E[Normal Execution]

🎯 Practical Example: Number Filter

Let’s find numbers divisible by 3, but stop if we hit 15:

for (int i = 1; i <= 20; i++)
{
    if (i == 15)
    {
        Console.WriteLine("Reached 15! Stopping.");
        break;
    }

    if (i % 3 != 0)
    {
        continue; // Skip non-divisible
    }

    Console.WriteLine(i + " is divisible by 3");
}

Output:

3 is divisible by 3
6 is divisible by 3
9 is divisible by 3
12 is divisible by 3
Reached 15! Stopping.

🎊 You Did It!

You’ve mastered the Traffic Controller of C#!

graph TD
    A[🏆 Control Flow Master] --> B[If-Else: Make Decisions]
    A --> C[Switch: Choose Paths]
    A --> D[Loops: Repeat Actions]
    A --> E[Break/Continue: Control Flow]

Quick Recap

Now YOUR code can make smart decisions and repeat actions like a pro! 🚀