Question

How to check if a number is a multiple of 9 using bitwise operators in C++

Answer 1

#include <iostream>

bool checkmMultipleOf9UsingBitwise(int n) {
    if (n == 0 || n == 9) {
        return true;
    }
    else if (n < 9) {
            return false;
    }
        else {
            /* 
                until n becomes either:
                    0 or 9 → return true (it's a multiple of 9)
                    < 9 but not equal to 0 or 9 → return false
            */
            return checkmMultipleOf9UsingBitwise((int)(n >> 3) - (int)(n & 7));
        }
}
 
int main()
{
    int num = 72; // 8 * 9
    
    if (checkmMultipleOf9UsingBitwise(num)) {
        std::cout << "The Number is multiple of 9 \n" << std::endl;
    }
    else {
        std::cout << "The Number is not multiple of 9 \n" << std::endl;
    }
}



/*
run:

The Number is multiple of 9 

*/

 

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