CODEWITHSUNDEEP
creversebit
ulysessg
ulysessg

Reputation: 11

Question on C program that reverses an unsigned integers bits

Hi all I am writing a C program that asks the user for an unsigned integer. The program will then call a function unsigned int reverse_bits(unsigned int n) This function should return an unsigned integer whose bits are the same as those of n but in reverse order. Print to screen the integer whose bits are in reverse order.

Example:

User enters:
12 (binary 16 bits is 0000000000001100)

Program print to screen:
12288 (0011000000000000)

This is the code i have but it does not output the right answer:


#include <stdio.h>

//function prototype
unsigned int reverse_bits(unsigned int n);


int main(void) {
    unsigned int n;
    unsigned int bits;

    printf("Enter an unsigned integer: ");
    scanf("%u",&n);
    
    bits = reverse_bits(n);
    
    printf("%u\n",bits);

    return 0;
}

unsigned int reverse_bits(unsigned int n) {
    unsigned int reverse = 0;
    while (n > 0) {
            reverse = reverse << 1;
            if((n & 1) == 1) {
                    reverse = reverse | 1;
            }
            n = n >> 1;
    }
    return reverse;
}

This does not give me 12288 when I enter 12, it gives me 3, what did I do wrong?

Upvotes: 0

Views: 342

Answers (1)

giusepped
giusepped

Reputation: 152

The result depends on how many bits an unsigned int is stored on your machine. It is usually 4 bytes (32 bits). So, in your case 12 (00000000000000000000000000001100 in binary) becames 805306368 (00110000000000000000000000000000 in binary).

Apart from that, you need to iterate over all bits of an unsigned int:

for (size_t i = 0; i < sizeof(unsigned int) * 8; i++) {
    reverse = reverse << 1;
    if((n & 1) == 1) {
        reverse = reverse | 1;
    }
    n = n >> 1;
}

Upvotes: 3

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