Question

How to sum the digits of the number 2^N in C++

Answer 1

#include <iostream>
#include <string>

std::string Calculate2PowerNAsString(int N) {
    // Calculate 2^N as a string for large numbers
    std::string result = "1";
     
    for (int i = 0; i < N; i++) {
        int carry = 0;
        for (auto &digit : result) {
            int num = (digit - '0') * 2 + carry;
            digit = (num % 10) + '0';
            carry = num / 10;
        }
        if (carry > 0) {
            result += (carry + '0');
        }
    }
     
    return result;
}
 
int sumOfDigits(int N) {
    std::string result = Calculate2PowerNAsString(N);
 
    // Sum the digits
    int sum = 0;
    for (char digit : result) {
        sum += (digit - '0');
    }
     
    return sum;
}
 
int main() {
    int N = 15;
    std::cout << "Sum of digits of 2^" << N << " is: " << sumOfDigits(N) << std::endl;
     
    N = 100;
    std::cout << "Sum of digits of 2^" << N << " is: " << sumOfDigits(N) << std::endl;
     
    N = 1000;
    std::cout << "Sum of digits of 2^" << N << " is: " << sumOfDigits(N) << std::endl;
}
 
       
       
/*
run:
       
Sum of digits of 2^15 is: 26
Sum of digits of 2^100 is: 115
Sum of digits of 2^1000 is: 1366
 
*/

 

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