C++ Program To Add Two Binary Strings

// C++ program to add two 
// binary strings
#include <bits/stdc++.h>
using namespace std;

// This function adds two binary strings 
// and return result as a third string
string addBinary(string A, string B)
{
    // If the length of string A is greater 
    // than the length of B then just swap 
    // the string by calling the same 
    // function and make sure to return 
    // the function otherwise recursion 
    // will occur which leads to calling 
    // the same function twice
    if (A.length() > B.length())
        return addBinary(B, A);

    // Calculating the difference between 
    // the length of the two strings.
    int diff = B.length() - A.length();

    // Initialise the padding string which 
    // is used to store zeroes that should 
    // be added as prefix to the string which 
    // has length smaller than the other string.
    string padding;
    for (int i = 0; i < diff; i++)
        padding.push_back('0');

    A = padding + A;
    string res;
    char carry = '0';

    for (int i = A.length() - 1; i >= 0; i--) 
    {
        // This if condition solves 110 111 
        // possible cases
        if (A[i] == '1' && B[i] == '1') 
        {
            if (carry == '1')
                res.push_back('1'), carry = '1';
            else
                res.push_back('0'), carry = '1';
        }

        // This if condition solves 000 001 
        // possible cases
        else if (A[i] == '0' && B[i] == '0') 
        {
            if (carry == '1')
                res.push_back('1'), carry = '0';
            else
                res.push_back('0'), carry = '0';
        }

        // This if condition solves 100 101 010 
        // 011 possible cases
        else if (A[i] != B[i]) 
        {
            if (carry == '1')
                res.push_back('0'), carry = '1';
            else
                res.push_back('1'), carry = '0';
        }
    }

    // If at the end their is carry then just  
    // add it to the result
    if (carry == '1')
        res.push_back(carry);
    // reverse the result
    reverse(res.begin(), res.end());

    // To remove leading zeroes
    int index = 0;
    while (index + 1 < res.length() && 
           res[index] == '0')
        index++;
    return (res.substr(index));
}

// Driver code
int main()
{
    string a = "1101", b = "100";
    cout << addBinary(a, b) << endl;
    return 0;
}