23. C# (break)

0. The Real Goal of This Lesson

break is
a mechanism that forces a loop to stop immediately.

Even if the loop condition is still true,
execution jumps outside the loop.

If you misunderstand this:

• Loop flow becomes unpredictable
• Early exit logic becomes messy
• Control structure design weakens

This is not about memorizing a keyword.

It is about understanding forced termination.

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The Core Meaning of break

break means:

“Stop this loop right now.”

It does not wait for the loop condition to become false.

It overrides the normal repetition flow.

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1. The Simplest Example — for + break

Full Runnable Code

using System;

class Program
{
    static void Main()
    {
        for (int i = 0; i < 100; i++)
        {
            if (i > 25)
            {
                break;
            }

            Console.WriteLine(i);
        }

        Console.WriteLine("Loop finished.");
        Console.ReadKey();
    }
}

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Execution Flow Analysis

Original expectation:

0 to 99

Actual behavior:

• Loop starts at 0
• Continues increasing
• When i > 25 becomes true
• break executes
• Loop stops immediately
• Execution continues after the loop

Output:

0
1
...
25
Loop finished.

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Why Not Just Use i < 26?

In this example, you could.

But break is used when:

An unexpected or dynamic condition appears during execution.

It represents:

Early termination inside the loop body.

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2. Real Scenario — Repeated User Input

Goal

• Ask the user for a number
• If it is greater than 10 → stop
• Otherwise → repeat
• Allow typing "stop" to exit immediately

---

do-while + break Example

using System;

class Program
{
    static void Main()
    {
        string input;
        int number;

        do
        {
            Console.WriteLine("Enter a number greater than 10 (or type 'stop'):");

            input = Console.ReadLine();

            if (input == "stop")
            {
                break;
            }

            number = int.Parse(input);

        } while (number <= 10);

        Console.WriteLine("Loop ended.");
        Console.ReadKey();
    }
}

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Execution Scenarios

Case 1: User enters 5

• 5 ≤ 10 → condition true
• Loop continues

---

Case 2: User enters 20

• 20 ≤ 10 → condition false
• Loop ends naturally

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Case 3: User enters "stop"

• input == "stop" → true
• break executes
• Loop ends immediately
• Condition is not evaluated

This is forced exit.

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Why break Is Sometimes Cleaner

You could combine conditions:

while (number <= 10 && input != "stop")

But as logic grows:

• Conditions become harder to read
• Intent becomes less obvious

Using break makes the intention explicit:

“In this situation, exit immediately.”

It separates:

Normal loop logic
from
Exceptional exit logic

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Structural Understanding

There are two ways a loop can end.

1. Natural Termination

The condition becomes false.

2. Forced Termination

break executes.

Both are valid.

But they represent different design decisions.

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Where Does break Stop?

break only exits the nearest enclosing loop.

Example:

for (int i = 0; i < 5; i++)
{
    while (true)
    {
        break; // exits only the while loop
    }
}

The outer for loop continues.

break does not exit multiple levels.

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The Risk of Overusing break

If used carelessly:

• Flow becomes harder to follow
• Debugging becomes more complex
• Structure weakens

Principle:

Use break when early termination is truly required.

Not as a shortcut for poor condition design.

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Mental Model You Must Build

Loops (while, for) define structured repetition.

break defines exceptional escape.

Repetition is the rule.

break is the override.

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Real-World Example — Searching in an Array

int[] numbers = { 1, 3, 5, 7, 9 };

for (int i = 0; i < numbers.Length; i++)
{
    if (numbers[i] == 5)
    {
        Console.WriteLine("Found 5!");
        break;
    }
}

Once the value is found:

There is no reason to continue iterating.

This improves clarity and efficiency.

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One-Line Summary

break is a control mechanism that immediately terminates a loop, even if its condition is still true.