Logical operators in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if both conditions are true.

C Sharp (C#)

bool result = (a > 5) [1] (b < 10);

Drag options to blanks, or click blank then click option'

A^

B||

C|

D&&

Attempts:

3 left

💡 Hint

Common Mistakes

Using || instead of && causes the condition to be true if either side is true.

The && operator checks if both conditions are true.

2fill in blank

medium

Complete the code to check if at least one condition is true.

C Sharp (C#)

bool result = (x == 0) [1] (y == 1);

Drag options to blanks, or click blank then click option'

A||

B^

C&

D&&

Attempts:

3 left

💡 Hint

Common Mistakes

Using && instead of || causes the condition to require both sides true.

The || operator returns true if either condition is true.

3fill in blank

hard

Fix the error in the code to negate the condition.

C Sharp (C#)

bool isFalse = [1](flag);

Drag options to blanks, or click blank then click option'

A!

Bflag

C!!

Dnot

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'not' keyword which is not valid in C#.

Using double exclamation marks (!!) which is invalid syntax.

The ! operator negates a boolean value in C#.

4fill in blank

hard

Fill both blanks to create a condition that is true only if a is true and b is false.

C Sharp (C#)

bool result = (a [1] true) [2] (b [3] false);

Drag options to blanks, or click blank then click option'

A==

B&&

C||

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using || instead of && changes the logic to 'or' instead of 'and'.

Using != instead of == for comparisons causes wrong results.

Use == to compare values, && to combine conditions with 'and', and != to check inequality.

5fill in blank

hard

Fill all three blanks to create a condition that is true if x is greater than 10 or y is less than 5 and z is not equal to 0.

C Sharp (C#)

bool check = (x [1] 10) [2] (y [3] 5) && (z != 0);

Drag options to blanks, or click blank then click option'

A>

B<

D||

Attempts:

3 left

💡 Hint

Common Mistakes

Using && instead of || changes the logic to require both conditions true.

Using >= or <= instead of > or < changes the condition meaning.

Use > to check if x is greater than 10, || for 'or', and < to check if y is less than 5.

Practice

1. Which logical operator in C# means AND and returns true only if both conditions are true?

easy

A. !

B. ||

C. &&

D. &

Solution

1. Step 1: Understand the meaning of logical AND

   The AND operator returns true only if both conditions it connects are true.

2. Step 2: Identify the C# symbol for AND

   In C#, the logical AND operator is written as &&, which checks both sides for true.

3. Final Answer:

   && -> Option C

4. Quick Check:

   AND operator = && [OK]

Hint: AND is &&, OR is ||, NOT is ! [OK]

Common Mistakes:

• Confusing & (bitwise AND) with && (logical AND)
• Mixing OR (||) with AND (&&)
• Using ! as AND operator

2. Which of the following is the correct syntax to negate a boolean variable isActive in C#?

easy

A. isActive = !!isActive;

B. isActive = !isActive;

C. isActive = ~isActive;

D. isActive = isActive!;

Solution

1. Step 1: Understand the NOT operator syntax

   The NOT operator in C# is ! and it negates a boolean value.

2. Step 2: Check the correct usage

   Using ! before the variable negates it, so isActive = !isActive; is correct.

3. Final Answer:

   isActive = !isActive; -> Option B

4. Quick Check:

   NOT operator = ! [OK]

Hint: Use ! before variable to negate boolean [OK]

Common Mistakes:

• Using double !! which is invalid in C#
• Using bitwise NOT ~ on booleans
• Placing ! after the variable

3. What is the output of this C# code?

bool a = true;
bool b = false;
Console.WriteLine(a || b && !a);

medium

A. True

B. False

C. Compilation error

D. Null

Solution

1. Step 1: Evaluate the expression inside WriteLine

   Operator precedence: ! has highest, then &&, then ||.
   Calculate !a = !true = false.
   Then b && !a = false && false = false.
   Finally a || (b && !a) = true || false = true.

2. Step 2: Determine output

   The expression evaluates to true, so Console.WriteLine prints True.

3. Final Answer:

   True -> Option A

4. Quick Check:

   Operator precedence: ! > && > ||, result = True [OK]

Hint: Remember ! > && > || precedence [OK]

Common Mistakes:

• Ignoring operator precedence
• Evaluating && before !
• Assuming output is false due to b being false

4. Find the error in this C# code snippet:

bool x = true;
bool y = false;
if (x || && y)
{
    Console.WriteLine("Yes");
}

medium

A. No error, code is correct

B. Incorrect use of || operator

C. Missing parentheses around conditions

D. Missing variable before && operator

Solution

1. Step 1: Analyze the if condition syntax

   The condition is written as x || && y, which is invalid because && needs two operands.

2. Step 2: Identify the missing operand

   Between || and && operators, there is no variable or expression before &&, causing syntax error.

3. Final Answer:

   Missing variable before && operator -> Option D

4. Quick Check:

   Logical operators need operands on both sides [OK]

Hint: Each operator needs two conditions [OK]

Common Mistakes:

• Writing operators without operands
• Assuming || and && can be chained without variables
• Missing parentheses but that is not the main error here

5. You want to check if a number n is between 10 and 20 inclusive in C#. Which condition correctly uses logical operators?

hard

A. if (n >= 10 && n <= 20)

B. if (n >= 10 || n <= 20)

C. if (n > 10 && n < 20)

D. if (!(n < 10 && n > 20))

Solution

1. Step 1: Understand the range condition

   To check if n is between 10 and 20 inclusive, n must be greater or equal to 10 AND less or equal to 20.

2. Step 2: Evaluate each option

   if (n > 10 && n < 20) excludes 10 and 20 because it uses > and <.
   if (n >= 10 || n <= 20) uses OR, which is true for almost all numbers.
   if (n >= 10 && n <= 20) correctly uses >= and <= with AND.
   if (!(n < 10 && n > 20)) negates an impossible condition and is incorrect.

3. Final Answer:

   if (n >= 10 && n <= 20) -> Option A

4. Quick Check:

   Inclusive range needs >= and <= with AND [OK]

Hint: Use && with >= and <= for inclusive range [OK]

Common Mistakes:

• Using || instead of && for range checks
• Using > and < instead of >= and <=
• Negating wrong conditions