04. C# (bool and Comparison Operators )

0) Goal of This Lesson

bool represents the result of a question,
and comparison operators are how we ask those questions in code.

This is not about memorizing syntax.
It’s about running the code and seeing how decisions start to appear.

1) What Is bool?

The bool type represents a Boolean value.

It can hold only two values:

• true
• false

bool isCorrect = true;
bool isFinished = false;

Key idea

• bool does not store data
• it stores the result of a condition
• the answer to a yes / no question

2) Why Do We Need bool?

Consider this question:

“Is the user input equal to ABC?”

This is not a number.
This is not a string.

👉 It’s a question.

So the result must be:

• true
• or false

3) Run This Example

using System;

class Program
{
    static void Main()
    {
        Console.WriteLine("Type something:");
        var userInput = Console.ReadLine();

        bool isEqualToAbc = userInput == "ABC";

        Console.WriteLine(isEqualToAbc);
    }
}

Try different inputs

• Input: ABC → Output: true
• Input: XYZ → Output: false

This is the first real decision your program makes.

4) = vs == (Very Important)

These two are not the same.

Assignment

userInput = "ABC";

• puts a value into a variable

Comparison

userInput == "ABC";

• asks a question
• returns a bool

📌 == always produces a bool.

5) Understanding by Observing (Runtime Thinking)

Instead of trusting the output, focus on this line:

bool isEqualToAbc = userInput == "ABC";

At runtime, this variable becomes:

• true if the input matches
• false if it doesn’t

This is how program logic begins.

6) Checking “Not Equal”

Using the inequality operator

bool isNotEqual = userInput != "ABC";

• != means “not equal”

Using logical negation

bool isEqual = userInput == "ABC";
bool isNotEqual = !isEqual;

• ! means NOT

📌 In practice, != is usually clearer and preferred.

7) Comparing Numbers

int number = 10;

bool greaterThan = number > 5;
bool smallerThan = number < 10;
bool greaterOrEqual = number >= 10;
bool smallerOrEqual = number <= 6;

Comparison operators

⚠️ Order matters:

=>  // ❌ invalid
>=  // ✅ correct

8) The % (Modulo) Operator

int number = 10;
bool isEven = number % 2 == 0;

What % means

The remainder after division

Examples:

• 10 % 3 → 1
• 10 % 2 → 0

Common real-world uses:

• even / odd checks
• periodic execution
• “every Nth time” logic

9) What Not to Think About Yet

❌ if statements
❌ full control flow
❌ complex logic

Right now, the goal is simpler:

One question → one bool

Examples:

• Is the input "ABC"?
• Is the number greater than 10?
• Is the value even?

10) 30-Second Self Check

Explain the results without running the code:

bool result1 = "ABC" == "ABC";
bool result2 = 10 > 20;
bool result3 = 10 % 2 == 0;

If you can explain why each is true or false,
👉 this lesson is complete.

One-Line Summary

bool doesn’t store data —
it stores the result of a condition.

This is the point where a C# program stops just running
and starts thinking.