Logical operators - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if both a and b are true using the logical AND operator.

C

if (a [1] b) {
    printf("Both are true\n");
}

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

A||

B|

C&&

D&

Attempts:

3 left

💡 Hint

Common Mistakes

Using | instead of && which is a bitwise OR, not logical AND.

Using || which checks if either condition is true, not both.

The logical AND operator in C is &&. It returns true only if both operands are true.

2fill in blank

medium

Complete the code to check if either x or y is true using the logical OR operator.

C

if (x [1] y) {
    printf("At least one is true\n");
}

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

A||

B|

C&

D&&

Attempts:

3 left

💡 Hint

Common Mistakes

Using & instead of || which is a bitwise AND, not logical OR.

Using && which requires both conditions to be true.

The logical OR operator in C is ||. It returns true if at least one operand is true.

3fill in blank

hard

Fix the error in the condition to check if not flag is true.

C

if ([1]flag) {
    printf("Flag is false\n");
}

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

A!

Bnot

Cflag

D~

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'not' which is not valid C syntax.

Using ~ which is bitwise NOT, not logical NOT.

The logical NOT operator in C is !. It negates the boolean value of flag.

4fill in blank

hard

Fill both blanks to check if a is true and b is false.

C

if (a [1] [2]b) {
    printf("a is true and b is false\n");
}

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

A&&

B||

C!

D~

Attempts:

3 left

💡 Hint

Common Mistakes

Using || instead of && which would check if either condition is true.

Using ~ instead of ! which is bitwise NOT.

Use && to check both conditions and ! to negate b.

5fill in blank

hard

Fill all three blanks to check if x is true, y is false, and z is true.

C

if (x [1] [2]y [3] z) {
    printf("x true, y false, z true\n");
}

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

A&&

B||

C!

D&

Attempts:

3 left

💡 Hint

Common Mistakes

Using | or & which are bitwise operators, not logical.

Using || which would allow any condition to be true.

Use && to combine conditions, ! to negate y, and && again to combine with z.

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 logical AND operator

   The logical AND operator (&&) returns true only if both conditions it connects are true.

2. Step 2: Compare with other operators

   The || operator means OR, ! means NOT, and & is bitwise AND, not logical AND.

3. Final Answer:

   && -> Option C

4. Quick Check:

   AND = && [OK]

Hint: AND operator is double ampersand && [OK]

Common Mistakes:

• Confusing & (bitwise) with && (logical)
• Mixing OR and AND operators
• Using ! for AND

2. Which of the following is the correct syntax to negate a condition in C?

easy

A. condition !

B. !condition

C. not condition

D. condition != true

Solution

1. Step 1: Identify negation syntax in C

   The NOT operator in C is a single exclamation mark placed before the condition: !condition.

2. Step 2: Check other options

   condition ! places ! after condition which is invalid, C uses 'not' which is not C syntax, D is a comparison, not negation.

3. Final Answer:

   !condition -> Option B

4. Quick Check:

   NOT = ! before condition [OK]

Hint: Negate condition with ! before it [OK]

Common Mistakes:

• Putting ! after condition
• Using 'not' keyword
• Confusing != with negation

3. What is the output of this C code?

int a = 5, b = 10;
if (a > 3 && b < 15) {
    printf("True\n");
} else {
    printf("False\n");
}

medium

A. No output

B. False

C. Compilation error

D. True

Solution

1. Step 1: Evaluate first condition (a > 3)

   a is 5, which is greater than 3, so this condition is true.

2. Step 2: Evaluate second condition (b < 15)

   b is 10, which is less than 15, so this condition is true.

3. Step 3: Apply logical AND (&&)

   Both conditions are true, so the combined condition is true, entering the if block.

4. Final Answer:

   True -> Option D

5. Quick Check:

   True && True = True [OK]

Hint: Both conditions true means && condition is true [OK]

Common Mistakes:

• Assuming OR instead of AND
• Misreading variable values
• Ignoring logical operator precedence

4. Find the error in this C code snippet:

int x = 0;
if (x = 5 || x == 0) {
    printf("Yes\n");
}

medium

A. Using assignment '=' instead of comparison '==' in if condition

B. Missing semicolon after printf statement

C. Incorrect use of logical AND instead of OR

D. Variable x is not declared

Solution

1. Step 1: Check the if condition syntax

   The condition uses 'x = 5 || x == 0'. The '=' is assignment, not comparison.

2. Step 2: Understand effect of assignment in condition

   Assignment returns the assigned value (5), which is true, so condition always true, likely a bug.

3. Final Answer:

   Using assignment '=' instead of comparison '==' in if condition -> Option A

4. Quick Check:

   Use '==' for comparison, not '=' [OK]

Hint: Use '==' to compare, '=' assigns value [OK]

Common Mistakes:

• Confusing '=' and '=='
• Ignoring logical operator precedence
• Assuming code won't compile

5. Given the code below, what will be printed?

int a = 0, b = 1, c = 2;
if (!(a || b) && c > 1) {
    printf("Inside if\n");
} else {
    printf("Inside else\n");
}

hard

A. Inside else

B. Inside if

C. Compilation error

D. No output

Solution

1. Step 1: Evaluate inner OR condition (a || b)

   a is 0 (false), b is 1 (true), so a || b is true.

2. Step 2: Apply NOT operator !(a || b)

   NOT true is false, so this part is false.

3. Step 3: Evaluate c > 1

   c is 2, which is greater than 1, so true.

4. Step 4: Combine with AND: false && true

   False AND anything is false, so condition is false, else block runs.

5. Final Answer:

   Inside else -> Option A

6. Quick Check:

   !(true) && true = false [OK]

Hint: NOT true is false; AND with false is false [OK]

Common Mistakes:

• Ignoring NOT operator effect
• Misreading OR condition
• Assuming if block runs when condition false