Check if Number is Power of Two in DSA C - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code snippet?

Given the function to check if a number is a power of two, what will be printed for n = 16?

DSA C

int isPowerOfTwo(unsigned int n) {
    return n && !(n & (n - 1));
}

#include <stdio.h>

int main() {
    unsigned int n = 16;
    if (isPowerOfTwo(n)) {
        printf("Yes\n");
    } else {
        printf("No\n");
    }
    return 0;
}

A No

B 1

C 0

D Yes

💡 Hint

A power of two has exactly one bit set in binary.

The function returns true if n is not zero and n & (n-1) is zero, which is true only for powers of two. 16 is 2^4, so output is 'Yes'.

❓ Predict Output

intermediate

What is the output when n = 0?

Using the same function, what will be printed for n = 0?

DSA C

int isPowerOfTwo(unsigned int n) {
    return n && !(n & (n - 1));
}

#include <stdio.h>

int main() {
    unsigned int n = 0;
    if (isPowerOfTwo(n)) {
        printf("Yes\n");
    } else {
        printf("No\n");
    }
    return 0;
}

A Yes

B 1

C No

D 0

💡 Hint

Zero is not a power of two.

The function returns false for zero because the first condition 'n' fails. So output is 'No'.

🔧 Debug

advanced

What error does this code raise?

Identify the error in this code snippet that attempts to check if n is a power of two.

DSA C

int isPowerOfTwo(unsigned int n) {
    return n & (n - 1) == 0;
}

#include <stdio.h>

int main() {
    unsigned int n = 8;
    if (isPowerOfTwo(n)) {
        printf("Yes\n");
    } else {
        printf("No\n");
    }
    return 0;
}

A Logical error causing wrong output

B Always prints 'No'

C No error, prints 'Yes'

D Syntax error

💡 Hint

Operator precedence matters in bitwise and comparison operations.

The expression 'n & (n - 1) == 0' is evaluated as 'n & ((n - 1) == 0)', which is wrong. It should be '(n & (n - 1)) == 0'.

🧠 Conceptual

advanced

How many numbers between 1 and 16 (inclusive) are powers of two?

Count how many numbers in the range 1 to 16 are powers of two.

A 5

B 4

C 6

D 7

💡 Hint

Powers of two are 1, 2, 4, 8, 16 in this range.

The powers of two in 1 to 16 are 1, 2, 4, 8, and 16, total 5 numbers.

🚀 Application

expert

What is the value of variable 'count' after this code runs?

This code counts how many numbers in an array are powers of two. What is the final count?

DSA C

#include <stdio.h>

int isPowerOfTwo(unsigned int n) {
    return n && !(n & (n - 1));
}

int main() {
    unsigned int arr[] = {3, 4, 6, 8, 16, 18, 32};
    int count = 0;
    for (int i = 0; i < 7; i++) {
        if (isPowerOfTwo(arr[i])) {
            count++;
        }
    }
    printf("%d\n", count);
    return 0;
}

A 3

B 4

C 5

D 6

💡 Hint

Check each number if it has exactly one bit set.

Numbers 4, 8, 16, and 32 are powers of two, so count is 4.