20. C# (Infinite Loops)

0. The Real Goal of This Lesson

A while loop repeats based on a condition,
but what actually stops the loop is state change.

The tools that create state change are:

• +=
• -=
• *=
• ++
• --

Without them, loops do not evolve.

They freeze.

And frozen state inside a loop is dangerous.

---

1. Start With a Basic Review

int number = 0;

while (number < 5)
{
    number = number + 1;
    Console.WriteLine(number);
}

This prints:

1
2
3
4
5

Why?

Because the state (number) changes every iteration.

---

2. The += Operator (Compound Assignment)

This line:

number = number + 1;

Can be simplified to:

number += 1;

It means:

Take the current value of number,
add 1,
and store the result back into number.

No logic change.

Only structural simplification.

---

3. Runnable Example — Increasing by 2

using System;

class Program
{
    static void Main()
    {
        int number = 0;

        while (number < 10)
        {
            number += 2;
            Console.WriteLine(number);
        }

        Console.WriteLine("Finished.");
        Console.ReadKey();
    }
}

Output:

2
4
6
8
10

The loop progresses because the state moves forward.

---

4. += Also Works With Strings

using System;

class Program
{
    static void Main()
    {
        string text = "ab";
        text += "cd";

        Console.WriteLine(text); // abcd
        Console.ReadKey();
    }
}

Strings can accumulate values.

This is still state change.

Different type.

Same principle.

---

5. Dangerous Code — Infinite Loop

Now the critical part.

Incorrect Example

using System;

class Program
{
    static void Main()
    {
        int number = 0;

        while (number < 10)
        {
            number *= 2;
            Console.WriteLine(number);
        }
    }
}

What happens?

The console keeps printing:

0
0
0
0
...

The program never stops.

---

6. Why Did This Happen?

Initial state:

number = 0

Inside the loop:

number *= 2;

0 × 2 = 0

The state does not change.

Condition:

0 < 10 → always true

The loop never reaches a false condition.

This is an infinite loop.

---

7. Definition of an Infinite Loop

A loop whose condition never becomes false.

The usual causes:

• No state change
• Incorrect state change
• Condition that can never fail

Infinite loops are logic failures.

Not syntax failures.

---

8. Fixing the Problem

Change the initial value:

int number = 1;

Now the flow becomes:

1 → 2 → 4 → 8 → 16

When number becomes 16:

16 < 10 → false

The loop exits correctly.

Termination restored.

---

9. The ++ Operator (Increment Operator)

This:

number += 1;

Can be shortened to:

number++;

It means:

Increase number by 1.

Same state change.

Cleaner syntax.

---

10. Pre-Increment vs Post-Increment (Simplified for Now)

number++;
++number;

Inside a loop body:

There is no visible difference.

The difference only matters when used inside expressions.

At this stage, treat them as equivalent for loop progression.

---

11. The Structural Model of a Loop

Every loop requires three components:

Component	Purpose
Condition	Decides whether to continue
State variable	Value used inside condition
State change	Mechanism that eventually makes the condition false

If one is missing:

• Infinite loop
• Immediate termination
• Logical inconsistency

Loops are not magic.

They are structured repetition systems.

---

12. A Critical Habit

Before writing any loop, ask:

“When does this loop stop?”

If you cannot answer that clearly,

Do not write the loop yet.

---

13. Practice Exercises

Implement the following using while:

1. Print numbers from 1 to 100
2. Increase by 2 each time
3. Print only multiples of 5
4. Count down from 100 to 0

Each one forces you to think about:

• Condition
• State
• State change

---

Final Summary

• += accumulates
• ++ increments by one
• Loops depend on state change
• Infinite loops are state change failures