Logical patterns (and, or, not) in C Sharp (C#) - Mini Project: Build & Apply

Logical patterns (and, not) in C#

📖 Scenario: You are building a simple security system that checks if a person can enter a building based on their ID badge and time of entry.

🎯 Goal: Create a program that uses logical patterns and and not to decide if entry is allowed.

📋 What You'll Learn

Create a boolean variable hasIDBadge with value true or false

Create an integer variable entryHour representing the hour of entry (0 to 23)

Create a boolean variable isWeekend to indicate if it is weekend

Use logical operators && (and) and ! (not) to check entry conditions

Print "Entry allowed" if conditions are met, otherwise print "Entry denied"

💡 Why This Matters

🌍 Real World

Security systems often check multiple conditions like ID badges and time to allow or deny access.

💼 Career

Understanding logical operators is essential for writing conditions in software development, especially in security, validation, and decision-making code.

1

Create initial variables

Create a boolean variable hasIDBadge and set it to true. Create an integer variable entryHour and set it to 14.

C Sharp (C#)

// Your code here

Hint

Use bool for true/false and int for numbers.

2

Add weekend variable

Add a boolean variable isWeekend and set it to false.

C Sharp (C#)

bool hasIDBadge = true;
int entryHour = 14;
// Your code here

Hint

Weekend means no workday, so set isWeekend to false for now.

3

Write entry condition using logical operators

Write an if statement that checks if hasIDBadge is true and entryHour is between 9 and 17 inclusive and it is not weekend (isWeekend is false). Use && for and and ! for not.

C Sharp (C#)

bool hasIDBadge = true;
int entryHour = 14;
bool isWeekend = false;

// Your code here

Hint

Use if (hasIDBadge && entryHour >= 9 && entryHour <= 17 && !isWeekend) to check all conditions.

4

Print the result

Inside the if block, write Console.WriteLine("Entry allowed"). Inside the else block, write Console.WriteLine("Entry denied").

C Sharp (C#)

bool hasIDBadge = true;
int entryHour = 14;
bool isWeekend = false;

if (hasIDBadge && entryHour >= 9 && entryHour <= 17 && !isWeekend)
{
    // Your code here
}
else
{
    // Your code here
}

Hint

Use Console.WriteLine to show the message on screen.

Practice

1.

Which logical operator in C# means both conditions must be true?

and, or, or not?

easy

A. and

B. or

C. not

D. xor

Solution

1. Step 1: Understand the meaning of logical operators

   The and operator requires both conditions to be true for the whole expression to be true.

2. Step 2: Compare with other operators

   or means one or both conditions are true, not negates a condition, and xor means exactly one condition is true.

3. Final Answer:

   and -> Option A

4. Quick Check:

   and means both true [OK]

Hint: Remember: and = both true, or = any true, not = reverse [OK]

Common Mistakes:

• Confusing 'and' with 'or'
• Thinking 'not' means both true
• Mixing 'xor' with 'and'

2.

Which of these is the correct C# syntax for the logical NOT operator?

?

easy

A. not x

B. x!

C. !x

D. ~x

Solution

1. Step 1: Recall C# logical NOT syntax

   In C#, the logical NOT operator is ! placed before the variable or expression.

2. Step 2: Check other options

   not x is not valid C# syntax, ~x is bitwise NOT, and x! is invalid.

3. Final Answer:

   !x -> Option C

4. Quick Check:

   Logical NOT uses ! before expression [OK]

Hint: Logical NOT is always ! before the variable [OK]

Common Mistakes:

• Using 'not' keyword instead of !
• Confusing bitwise ~ with logical !
• Placing ! after the variable

3.

What is the output of this C# code?

bool a = true;
bool b = false;
if (a && !b) {
    Console.WriteLine("Yes");
} else {
    Console.WriteLine("No");
}

medium

A. No

B. Yes

C. True

D. False

Solution

1. Step 1: Evaluate variables and conditions

   Variable a is true, b is false, so !b is true.

2. Step 2: Evaluate the if condition

   a && !b becomes true && true, which is true, so the if block runs.

3. Final Answer:

   Yes -> Option B

4. Quick Check:

   true and not false = true [OK]

Hint: Remember ! reverses boolean, so !false = true [OK]

Common Mistakes:

• Ignoring the ! operator
• Thinking false && true is true
• Confusing output strings with boolean values

4.

Find the error in this C# code snippet:

bool x = true;
if (x && !x) {
    Console.WriteLine("True");
} else {
    Console.WriteLine("False");
}

medium

A. Using single & instead of &&

B. Missing semicolon after if statement

C. Incorrect use of Console.WriteLine

D. Contradictory condition: x and not x can never be true

Solution

1. Step 1: Analyze the condition logic

   The condition x && !x means x is true AND x is false at the same time, which is impossible.

2. Step 2: Check syntax correctness

   The syntax is correct: && is used properly, semicolons and Console.WriteLine are fine.

3. Final Answer:

   Contradictory condition: x and not x can never be true -> Option D

4. Quick Check:

   True and not true = false always [OK]

Hint: Check if condition can ever be true logically [OK]

Common Mistakes:

• Thinking condition can be true
• Confusing & with &&
• Looking for syntax errors when logic is the issue

5.

You want to write a C# switch expression that returns "Valid" only if age is between 18 and 30 inclusive, and hasID is true. Which pattern correctly uses logical operators?

return (age, hasID) switch {
    ??? => "Valid",
    _ => "Invalid"
};

hard

A. var (a, id) when a >= 18 && a <= 30 && id

B. (>= 18 and <= 30 and true, hasID)

C. var a when a >= 18 && a <= 30 && hasID == true

D. (>= 18 and <= 30, true)

Solution

1. Step 1: Understand switch pattern matching with tuples

   The switch matches a tuple (age, hasID). To check conditions on both, use a when clause with logical operators.

2. Step 2: Analyze each option

   var (a, id) when a >= 18 && a <= 30 && id correctly uses tuple deconstruction var (a, id) and checks a >= 18 && a <= 30 && id (where id is boolean). Others are invalid syntax or misuse logical operators.

3. Final Answer:

   var (a, id) when a >= 18 && a <= 30 && id -> Option A

4. Quick Check:

   Tuple pattern with when and && is correct [OK]

Hint: Use tuple deconstruction with when and && for multiple conditions [OK]

Common Mistakes:

• Trying to use and inside tuple without when
• Misplacing logical operators outside when clause
• Not deconstructing tuple properly