Bitwise NOT in C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to apply the bitwise NOT operator to the variable num.

C

int num = 5;
int result = [1]num;
printf("%d\n", result);

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 NOT (~).

Using bitwise OR (|) or XOR (^) operators.

The bitwise NOT operator in C is the tilde symbol ~. It flips all bits of the number.

2fill in blank

medium

Complete the code to print the bitwise NOT of the variable value.

C

int value = 0;
int inverted = [1]value;
printf("%d\n", inverted);

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

A&

B^

C~

D|

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using bitwise AND (&) or OR (|) by mistake.

The bitwise NOT operator is ~, which flips all bits of the integer.

3fill in blank

hard

Fix the error in the code to correctly compute the bitwise NOT of x.

C

int x = 12;
int y = [1] x;
printf("%d\n", y);

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

A~

B!

C&

D|

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using bitwise AND (&) or OR (|) operators.

The bitwise NOT operator is ~. Using ! is logical NOT, which is incorrect here.

4fill in blank

hard

Fill both blanks to create a dictionary-like structure using a struct and apply bitwise NOT to val.

C

struct Data {
    int val;
};

struct Data d = {10};
int inverted = [1]d.[2];
printf("%d\n", inverted);

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

A~

B!

Cval

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using incorrect member name like value.

Use the tilde (~) for bitwise NOT and access the member val of the struct.

5fill in blank

hard

Fill all three blanks to create a function that returns the bitwise NOT of its integer parameter.

C

int bitwiseNot(int [1]) {
    return [2][3];
}

int main() {
    int num = 7;
    printf("%d\n", bitwiseNot(num));
    return 0;
}

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

Ax

B~

Dnum

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in parameter and return.

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

The function parameter is x. The return statement applies bitwise NOT (~) to x.

Practice

1. What does the bitwise NOT operator ~ do to an integer in C?

easy

A. It adds 1 to the integer.

B. It shifts all bits to the left by one position.

C. It sets all bits to zero.

D. It flips every bit of the integer, changing 0s to 1s and 1s to 0s.

Solution

1. Step 1: Understand the bitwise NOT operator

   The bitwise NOT operator ~ in C flips every bit of the integer. This means all 0 bits become 1, and all 1 bits become 0.

2. Step 2: Compare with other bitwise operations

   Unlike shifting or adding, ~ only toggles bits without changing their positions or values numerically.

3. Final Answer:

   It flips every bit of the integer, changing 0s to 1s and 1s to 0s. -> Option D

4. Quick Check:

   Bitwise NOT = flip bits [OK]

Hint: Remember: ~ flips bits, not shifts or adds [OK]

Common Mistakes:

• Confusing ~ with bit shift operators << or >>
• Thinking ~ adds or subtracts from the number
• Assuming ~ sets bits to zero instead of flipping

2. Which of the following is the correct syntax to apply bitwise NOT to an integer variable x in C?

easy

A. int y = ~x;

B. int y = not x;

C. int y = !x;

D. int y = x~;

Solution

1. Step 1: Recall the bitwise NOT operator syntax

   In C, the bitwise NOT operator is the tilde symbol ~ placed before the variable.

2. Step 2: Check each option

   int y = not x; uses not which is not valid in C. int y = !x; uses logical NOT !. int y = x~; has incorrect placement of ~. Only int y = ~x; correctly uses ~x.

3. Final Answer:

   int y = ~x; -> Option A

4. Quick Check:

   Bitwise NOT syntax = ~x [OK]

Hint: Use ~ before variable for bitwise NOT [OK]

Common Mistakes:

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

3. What is the output of the following C code?

int x = 5;
int y = ~x;
printf("%d", y);

medium

A. 5

B. -6

C. -5

D. 6

Solution

1. Step 1: Convert 5 to binary and apply bitwise NOT

   5 in binary (32-bit) is 00000000 00000000 00000000 00000101. Applying ~ flips bits to 11111111 11111111 11111111 11111010.

2. Step 2: Interpret the result as a signed integer

   The result is the two's complement representation of -6.

3. Final Answer:

   -6 -> Option B

4. Quick Check:

   ~5 = -6 in two's complement [OK]

Hint: ~x equals -(x+1) for signed integers [OK]

Common Mistakes:

• Thinking ~5 equals 6 instead of -6
• Ignoring two's complement representation
• Confusing bitwise NOT with logical NOT

4. Identify the error in the following C code snippet:

int x = 10;
int y = ~ x;
printf("%d", y);

medium

A. There is a syntax error due to space between ~ and x.

B. The code will print 9 instead of expected -11.

C. No error; the code works and prints -11.

D. The printf format specifier is incorrect.

Solution

1. Step 1: Check syntax of bitwise NOT usage

   In C, spaces between operators and operands are allowed. So ~ x is valid and equivalent to ~x.

2. Step 2: Verify output and printf usage

   Applying ~10 results in -11. The printf format specifier %d is correct for int.

3. Final Answer:

   No error; the code works and prints -11. -> Option C

4. Quick Check:

   Space allowed after ~, output = -11 [OK]

Hint: Spaces don't break ~ operator usage [OK]

Common Mistakes:

• Thinking space causes syntax error
• Expecting positive output instead of negative
• Confusing format specifier for int

5. Given a signed 8-bit integer n, which expression correctly computes the bitwise NOT of n and then adds 1, effectively calculating the two's complement negation of n in C?

hard

A. ~n + 1

B. ~(n + 1)

C. -~n

D. -n + 1

Solution

1. Step 1: Understand two's complement negation

   Two's complement negation of a number n is computed as ~n + 1.

2. Step 2: Analyze each option

   ~n + 1 matches the formula. ~(n + 1) negates after adding 1, which is incorrect. -~n negates the bitwise NOT, not the number. -n + 1 is arithmetic negation plus 1, which is not two's complement negation.

3. Final Answer:

   ~n + 1 -> Option A

4. Quick Check:

   Two's complement negation = ~n + 1 [OK]

Hint: Two's complement negation = ~n + 1 [OK]

Common Mistakes:

• Using -(~n) instead of ~n + 1
• Applying ~ after adding 1
• Confusing arithmetic negation with bitwise negation