Logical operators in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if both conditions are true.

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 bitwise AND (&) instead of logical AND (&&).

Using logical OR (||) when both conditions must be true.

The logical AND operator && returns true only if both conditions are true.

2fill in blank

medium

Complete the code to check if either condition is true.

C++

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

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

A&&

B&

C!

D||

Attempts:

3 left

💡 Hint

Common Mistakes

Using logical AND (&&) when only one condition needs to be true.

Using bitwise OR (|) instead of logical OR (||).

The logical OR operator || returns true if at least one condition is true.

3fill in blank

hard

Fix the error in the condition to correctly negate the expression.

C++

if ([1]) {
    // do something
}

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

A!flag

B~flag

C!!flag

Dflag

Attempts:

3 left

💡 Hint

Common Mistakes

Using bitwise NOT (~) instead of logical NOT (!).

Not negating the flag when needed.

The logical NOT operator ! negates the boolean value of flag.

4fill in blank

hard

Fill both blanks to create a condition that is true only if a is positive and b is not zero.

C++

if ((a [1] 0) [2] (b != 0)) {
    // code here
}

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

A>

B&&

C||

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using logical OR (||) instead of AND (&&) when both conditions must be true.

Using less than (<) instead of greater than (>) for positive check.

The condition checks if a is greater than zero and b is not zero using logical AND &&.

5fill in blank

hard

Fill all three blanks to create a condition that is true if x is zero or y is positive and z is false.

C++

if ((x [1] 0) [2] (y [3] 0 && !z)) {
    // action
}

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

A==

B||

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using logical AND (&&) instead of OR (||) between x and y conditions.

Using less than (<) instead of greater than (>) for y check.

The condition checks if x equals zero or (y is greater than zero and z is false).

Practice

1. Which logical operator in C++ means "both conditions must be true"?

easy

A. &&

B. ||

C. !

D. &

Solution

1. Step 1: Understand the meaning of logical AND

   The operator that requires both conditions to be true is called logical AND.

2. Step 2: Identify the C++ symbol for logical AND

   In C++, logical AND is represented by &&.

3. Final Answer:

   && -> Option A

4. Quick Check:

   Both true = true means && [OK]

Hint: && means both true; || means one true [OK]

Common Mistakes:

• Confusing & (bitwise AND) with && (logical AND)
• Thinking || means both true
• Mixing ! with AND or OR

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

easy

A. !flag = flag;

B. flag = flag!;

C. flag != flag;

D. flag = !flag;

Solution

1. Step 1: Recall the negation operator syntax

   The negation operator ! is placed before the variable to flip its value.

2. Step 2: Check correct assignment syntax

   To update flag to its negation, write flag = !flag; which is valid C++ syntax.

3. Final Answer:

   flag = !flag; -> Option D

4. Quick Check:

   Negate with ! before variable [OK]

Hint: Put ! before variable to negate [OK]

Common Mistakes:

• Placing ! after variable (invalid syntax)
• Using != which means not equal
• Trying to assign to !flag (not a variable)

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

bool a = true;
bool b = false;
if (a || b) {
  std::cout << "Yes";
} else {
  std::cout << "No";
}

medium

A. Yes

B. No

C. true

D. false

Solution

1. Step 1: Evaluate the logical OR condition

   a is true, b is false, so a || b is true because at least one is true.

2. Step 2: Determine which branch runs

   Since the condition is true, the if block runs and prints "Yes".

3. Final Answer:

   Yes -> Option A

4. Quick Check:

   true || false = true [OK]

Hint: || is true if any side is true [OK]

Common Mistakes:

• Thinking both must be true for ||
• Confusing output with boolean literals
• Ignoring that std::cout prints strings

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

bool x = true;
bool y = false;
if (x & y) {
  std::cout << "True";
} else {
  std::cout << "False";
}

medium

A. Incorrect use of std::cout

B. Missing semicolon after bool declarations

C. Using & instead of && in if condition

D. Variables x and y not initialized

Solution

1. Step 1: Identify the operator used in condition

   The code uses & which is bitwise AND, not logical AND.

2. Step 2: Explain why && is needed

   For boolean logic in conditions, && should be used to combine true/false values.

3. Final Answer:

   Using & instead of && in if condition -> Option C

4. Quick Check:

   Logical AND needs && not & [OK]

Hint: Use && for logic, & is bitwise [OK]

Common Mistakes:

• Confusing bitwise & with logical &&
• Assuming & works like && in conditions
• Ignoring operator precedence differences

5. Given int a = 5; and int b = 10;, which condition correctly checks if a is less than 10 AND b is greater than 5?

hard

A. if (a < 10 || b > 5)

B. if (a < 10 && b > 5)

C. if (!(a < 10) && !(b > 5))

D. if (a > 10 && b < 5)

Solution

1. Step 1: Understand the condition requirements

   We want both: a less than 10 AND b greater than 5.

2. Step 2: Match condition with logical AND

   Logical AND (&&) combines both conditions to be true simultaneously.

3. Final Answer:

   if (a < 10 && b > 5) -> Option B

4. Quick Check:

   Both true means && [OK]

Hint: Use && to require both conditions true [OK]

Common Mistakes:

• Using || which means either condition true
• Negating conditions incorrectly
• Swapping comparison operators