Question

How to sum two binary strings in C++

Answer 1

#include <iostream>
#include <algorithm>

std::string addBinaryStrings(std::string a, std::string b) {
    std::string result;
    int i = a.length() - 1;
    int j = b.length() - 1;
    int carry = 0;

    while (i >= 0 || j >= 0) {
        int sum = carry;
        if (i >= 0) sum += a[i--] - '0';
        if (j >= 0) sum += b[j--] - '0';
        
        carry = sum > 1 ? 1 : 0;
        
        result.push_back(sum % 2 + '0');
    }

    if (carry != 0) result.push_back(carry + '0');
    
    std::reverse(result.begin(), result.end());
    
    return result;
}

int main() {
    std::string a = "11";
    std::string b = "1";
    std::cout << addBinaryStrings(a, b) << std::endl;

    a = "1010";
    b = "1011";
    std::cout << addBinaryStrings(a, b) << std::endl;
}

    
    
/*
run:
    
100
10101
 
*/

 

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Answer 2

#include <iostream>
#include <string>
#include <bitset>

std::string addBinaryStrings(std::string a, std::string b) {
    int num1 = std::stoi(a, nullptr, 2);
    int num2 = std::stoi(b, nullptr, 2);
    
    int sum = num1 + num2;
    
    return std::bitset<16>(sum).to_string();
}

int main() {
    std::string a = "11";
    std::string b = "1";
    std::cout << addBinaryStrings(a, b) << std::endl;
    
    a = "1010";
    b = "1011";
    std::cout << addBinaryStrings(a, b) << std::endl;
}



    
    
/*
run:
    
0000000000000100
0000000000010101
 
*/

 

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