Bit Manipulation Basics AND OR XOR NOT Left Right Shift in DSA Javascript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Bitwise AND and OR Operations

What is the output of the following JavaScript code?

const a = 5;  // binary 0101
const b = 3;  // binary 0011
const result = (a & b) | (a | b);
console.log(result);

DSA Javascript

const a = 5;  // binary 0101
const b = 3;  // binary 0011
const result = (a & b) | (a | b);
console.log(result);

A 3

B 5

C 7

D 1

💡 Hint

Remember how AND (&) and OR (|) work bit by bit.

AND of 5 (0101) and 3 (0011) is 1 (0001). OR of 5 and 3 is 7 (0111). Then OR of 1 and 7 is 7.

❓ Predict Output

intermediate

Effect of XOR on Bits

What will be printed by this JavaScript code?

const x = 12;  // binary 1100
const y = 10;  // binary 1010
const z = x ^ y;
console.log(z);

DSA Javascript

const x = 12;  // binary 1100
const y = 10;  // binary 1010
const z = x ^ y;
console.log(z);

A 2

B 6

C 14

D 8

💡 Hint

XOR (^) sets bits where bits differ.

12 (1100) XOR 10 (1010) is 0110 in binary, which is 6 in decimal.

❓ Predict Output

advanced

Understanding NOT and Left Shift

What is the output of this JavaScript code?

const num = 4;  // binary 00000100
const result = (~num) << 1;
console.log(result);

DSA Javascript

const num = 4;  // binary 00000100
const result = (~num) << 1;
console.log(result);

A -10

B -8

C 10

D 8

💡 Hint

Remember NOT (~) flips all bits and left shift multiplies by 2.

NOT 4 flips bits to -5 (in two's complement). Left shifting -5 by 1 multiplies by 2, resulting in -10.

❓ Predict Output

advanced

Right Shift on Negative Number

What will this JavaScript code print?

const n = -16;
const shifted = n >> 2;
console.log(shifted);

DSA Javascript

const n = -16;
const shifted = n >> 2;
console.log(shifted);

A -4

B -5

C 3

D 12

💡 Hint

Right shift on negative numbers keeps the sign bit.

Right shifting -16 by 2 divides by 4 rounding down, resulting in -4.

🧠 Conceptual

expert

Number of Set Bits After Multiple Bitwise Operations

Given the code below, how many bits are set to 1 in the final value of res?

let a = 29;   // binary 00011101
let b = 23;   // binary 00010111
let res = (a & b) ^ (~a | b);

DSA Javascript

let a = 29;   // binary 00011101
let b = 23;   // binary 00010111
let res = (a & b) ^ (~a | b);

A 4

B 6

C 3

D 5

💡 Hint

Calculate each part step by step in binary, then count 1s in the final result.

a & b = 21 (00010101), ~a = -30 (two's complement), ~a | b = -6, XOR with 21 results in -27, which in 32-bit binary has 5 bits set to 1.

Practice

1. What is the result of the bitwise AND operation between 5 and 3? (5 & 3)

easy

A. 1

B. 7

C. 0

D. 8

Solution

1. Step 1: Convert numbers to binary

   5 in binary is 0101, 3 in binary is 0011.

2. Step 2: Perform bitwise AND

   0101 & 0011 = 0001 (only bits set in both numbers remain set).

3. Final Answer:

   1 -> Option A

4. Quick Check:

   5 & 3 = 1 [OK]

Hint: AND keeps bits set in both numbers only [OK]

Common Mistakes:

• Confusing AND with OR operation
• Not converting numbers to binary before operation
• Assuming decimal addition instead of bitwise

2. Which of the following is the correct syntax for performing a bitwise XOR operation between variables a and b in JavaScript?

easy

A. let result = a | b;

B. let result = a && b;

C. let result = a % b;

D. let result = a ^ b;

Solution

1. Step 1: Identify bitwise XOR operator in JavaScript

   The XOR operator is represented by the caret symbol (^).

2. Step 2: Check syntax correctness

   let result = a ^ b; uses a ^ b, which is the correct syntax for bitwise XOR.

3. Final Answer:

   let result = a ^ b; -> Option D

4. Quick Check:

   XOR operator is ^ in JavaScript [OK]

Hint: XOR uses ^ symbol in JavaScript [OK]

Common Mistakes:

• Using && which is logical AND, not bitwise
• Using | which is bitwise OR, not XOR
• Using % which is modulo, unrelated to bits

3. What will be the output of the following JavaScript code?

let x = 8; // binary 1000
let y = x >> 2;
console.log(y);

medium

A. 2

B. 4

C. 1

D. 0

Solution

1. Step 1: Understand right shift operation

   Right shift by 2 means move bits 2 places to the right, dropping the rightmost bits.

2. Step 2: Apply right shift on binary 1000

   1000 >> 2 becomes 0010, which is decimal 2.

3. Final Answer:

   2 -> Option A

4. Quick Check:

   8 >> 2 = 2 [OK]

Hint: Right shift divides by 2 for each shift [OK]

Common Mistakes:

• Confusing right shift with left shift
• Not converting binary to decimal after shift
• Assuming shift adds zeros on left without dropping bits

4. Find the error in the following code snippet that attempts to flip all bits of a number n using bitwise NOT:

let n = 5;
let flipped = ~n;
console.log(flipped);

What is the issue?

medium

A. Missing parentheses around ~n

B. Bitwise NOT returns a negative number due to two's complement representation

C. Variable n must be a string for bitwise NOT

D. Bitwise NOT operator (~) is not supported in JavaScript

Solution

1. Step 1: Understand bitwise NOT in JavaScript

   Bitwise NOT flips all bits and returns the two's complement negative number.

2. Step 2: Explain why output is negative

   For 5 (00000101), ~5 flips bits to 11111010 which is -6 in two's complement.

3. Final Answer:

   Bitwise NOT returns a negative number due to two's complement representation -> Option B

4. Quick Check:

   ~n flips bits and returns negative number [OK]

Hint: Bitwise NOT flips bits and returns negative in JS [OK]

Common Mistakes:

• Expecting positive flipped bits as output
• Thinking ~ is unsupported operator
• Assuming input must be string for bitwise ops

5. You want to set the 3rd bit (0-indexed from right) of a number num to 1 without changing other bits. Which expression correctly does this in JavaScript?

hard

A. num = num ^ (1 << 3);

B. num = num & (1 << 3);

C. num = num | (1 << 3);

D. num = num << 3;

Solution

1. Step 1: Understand setting a bit using OR and shift

   Left shift 1 by 3 gives 00001000, which targets the 3rd bit.

2. Step 2: Use OR to set the bit without changing others

   OR with this mask sets the 3rd bit to 1, keeping others unchanged.

3. Final Answer:

   num = num | (1 << 3); -> Option C

4. Quick Check:

   Use OR with shifted 1 to set bit [OK]

Hint: Use OR with (1 << bit_position) to set bit [OK]

Common Mistakes:

• Using AND which clears bits instead of setting
• Using XOR which toggles bits and may unset
• Using left shift alone which changes number value