# Program to add two binary strings, and return also as binary string in C++

Suppose we have two binary strings a and b, we have to add these binary numbers and find their sum, also as a string.

So, if the input is like a = "10110", b = "10010", then the output will be "101000".

To solve this, we will follow these steps −

• ret := empty string
• na := size of a, nb := size of b
• i := na - 1, j := nb - 1
• carry := 0
• while (i >= 0 or j >= 0), do:
• addA := (if i >= 0, then a[i] - ASCII of '0', otherwise 0)
• addB := (if j >= 0, then b[j] - ASCII of '0', otherwise 0)
• carry := sum / 2
• sum := sum mod 2
• ret := ret concatenate sum
• (decrease i by 1)
• (decrease j by 1)
• if carry is non-zero, then:
• ret := ret concatenate carry
• reverse the array ret
• return ret

Let us see the following implementation to get better understanding −

## Example

Live Demo

#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
string solve(string a, string b){
string ret = "";
int na = a.size();
int nb = b.size();
int i = na - 1;
int j = nb - 1;
int carry = 0;
while(i >= 0 || j >= 0){
int addA = i >= 0 ? a[i] - '0' : 0;
int addB = j >= 0 ? b[j] - '0' : 0;
carry = sum / 2;
sum %= 2;
ret += to_string(sum);
i--;
j--;
}
if(carry)
ret += to_string(carry); reverse(ret.begin(), ret.end());
return ret;
}
};
main(){
string a = "10110", b = "10010"; Solution ob;
cout << ob.solve(a, b);
}

## Input

"10110","10010"

## Output

101000

Updated on: 05-Oct-2020

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