Check if Number is Even or Odd Using Bits in DSA C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the least significant bit (LSB) of a binary number tell us about the number?

The least significant bit (LSB) tells us if the number is even or odd. If LSB is 0, the number is even; if LSB is 1, the number is odd.

beginner

How can you check if a number is even using bitwise AND in C?

Use the expression (number & 1). If the result is 0, the number is even; if it is 1, the number is odd.

intermediate

Why is using bitwise operations to check even or odd numbers efficient?

Bitwise operations work directly on binary digits and are faster than division or modulus operations, making them efficient for checking even or odd.

beginner

What is the output of this C code snippet? <br>

int n = 6; if (n & 1) printf("Odd"); else printf("Even");

The output is "Even" because 6 in binary ends with 0, so (6 & 1) is 0.

intermediate

Explain the difference between using modulus (%) and bitwise AND (&) to check even or odd.

Modulus (%) divides the number and checks the remainder, which is slower. Bitwise AND (&) checks the last bit directly, which is faster and uses less CPU.

Which bitwise operation is used to check if a number is even or odd?

A NOT (~)

B AND (&) with 1

C XOR (^) with 1

D OR (|) with 1

AND (&) with 1 isolates the least significant bit to check if the number is even or odd.

What does the expression (number & 1) return if the number is odd?

A 0

B number itself

C -1

D 1

For odd numbers, the least significant bit is 1, so (number & 1) returns 1.

Why might bitwise checking be preferred over modulus for even/odd checks in embedded systems?

A Bitwise is faster and uses less CPU

B Bitwise is slower but more readable

C Bitwise uses less memory

D Modulus is not supported in embedded systems

Bitwise operations are faster and use less CPU, which is important in resource-limited embedded systems.

What is the output of this code? <br>

int x = 7; if (x & 1) printf("Odd"); else printf("Even");

A Odd

B Even

C 7

D Error

7 is odd, so (7 & 1) is 1, printing "Odd".

If (number & 1) == 0, what can we say about the number?

A It is odd

B It is negative

C It is even

D It is zero

If the least significant bit is 0, the number is even.

Describe how to check if a number is even or odd using bitwise operations in C.

Think about the last bit in binary.

Explain why bitwise operations are efficient for checking even or odd numbers compared to modulus.

Consider how computers handle bits versus division.