Program to add two binary strings in C++

Given two strings with binary number, we have to find the result obtained by adding those two binary strings and return the result as a binary string.

Binary numbers are those numbers which are expressed either as 0 or 1. While adding 2 binary numbers there is binary addition rule which is to be taken care of.

0+0 → 0
0+1 → 1
1+0 → 1
1+1 → 0, carry 1

Input

str1 = {“11”}, str2 = {“1”}

Output

“100”

Input

str1 = {“110”}, str2 = {“1”}

Output

“111”

Approach used below is as follows to solve the problem

Traverse both the string from last
Add the binary of two numbers
If there are two 1’s then make it zero and carry 1.
Return the result.

Algorithm

Start
Step 1→ declare function to add two strings
   string add(string a, string b)
      set string result = ""
      set int temp = 0
      set int size_a = a.size() – 1
      set int size_b = b.size() – 1
      While (size_a >= 0 || size_b >= 0 || temp == 1)
         Set temp += ((size_a >= 0)? a[size_a] - '0': 0)
         Set temp += ((size_b >= 0)? b[size_b] - '0': 0)
         Calculate result = char(temp % 2 + '0') + result
         Set temp /= 2
         Set size_a—
         Set size_b—
      End
      return result
Step 2→ In main()
   Declare string a = "10101", b="11100"
   Call add(a, b)
Stop

Example

Live Demo

#include<bits/stdc++.h>
using namespace std;
//function to add two strings
string add(string a, string b){
   string result = "";
   int temp = 0;
   int size_a = a.size() - 1;
   int size_b = b.size() - 1;
   while (size_a >= 0 || size_b >= 0 || temp == 1){
      temp += ((size_a >= 0)? a[size_a] - '0': 0);
      temp += ((size_b >= 0)? b[size_b] - '0': 0);
      result = char(temp % 2 + '0') + result;
      temp /= 2;
      size_a--; size_b--;
   }
   return result;
}
int main(){
   string a = "10101", b="11100";
   cout<<"sum of strings are : "<<add(a, b);
   return 0;
}