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C++ Program to Add Two Binary Numbers

In this article, you'll learn and get code for the addition of two binary numbers entered by the user at run-time. Here I've created programs for binary number addition in the following ways:

Note: If you don't know the basic rules of binary number addition, you can refer to its separate tutorial.

In C++, add binary numbers using the string data type

The question is: write a program in C++ that receives two binary numbers as input and finds and prints their addition. The program given below uses string data types to do the task. The size() function returns the length of a string.

#include<iostream>
using namespace std;

int main()
{
   string bin1, bin2, addRes;
   int len, carry, re, i;
   cout<<"Enter First Binary Number: ";
   cin>>bin1;
   cout<<"Enter Second Binary Number: ";
   cin>>bin2;
   len = bin1.size();
   addRes = "";
   carry = 0;
   for(i=(len-1); i>-1; i--)
   {
      re = carry;
      if(bin1[i] == '1')
         re = re+1;
      else
         re = re+0;
      if(bin2[i] == '1')
         re = re+1;
      else
         re = re+0;
      if(re%2==1)
         addRes = '1' + addRes;
      else
         addRes = '0' + addRes;
      if(re<2)
         carry = 0;
      else
         carry = 1;
   }
   if(carry!=0)
      addRes = '1' + addRes;
   cout<<"\nAddition Result = "<<addRes;
   return 0;
}

Here is the initial output produced by the above C++ program:

c++ add two binary numbers

Now enter 11101 as the first binary number and 11111 as the second. Here is its sample run with these user inputs:

binary number addition in c++

The dry run of the above program with the same user input, that is, 11101 and 11111 as two binary numbers, goes like this:

Note: The above program has a limitation. The limitation is that if the length of two entered binary inputs is not the same or equal, the program doesn't work correctly. Therefore, here is another program created that works in all conditions, whether the length of binary number inputs is equal or not.

#include<iostream>
using namespace std;

int main()
{
   string str1, str2, sum="";
   int len1, len2, i, j, ds=0;
   cout<<"Enter the First Binary Number: ";
   cin>>str1;
   cout<<"Enter the Second Binary Number: ";
   cin>>str2;
   len1 = str1.size();
   len2 = str2.size();
   i = len1 - 1;
   j = len2 - 1;
   while(i>=0 || j>=0 || ds==1)
   {
      ds = ds + ((i >= 0) ? str1[i] - '0' : 0);
      ds = ds + ((j >= 0) ? str2[j] - '0' : 0);
      sum = char(ds % 2 + '0') + sum;
      ds = ds/2;
      i--;
      j--;
   }
   cout<<"\nSum = "<<sum;
   return 0;
}

Here is its sample run with user inputs 10110 and 110 as two binary numbers:

add two binary numbers in c++

In C++, addition of a binary number using the int data type

This is the program you need, I think. Because this program does not use any string type to do the task. This program is created with all its variables as int types. However, the output of both programs is identical.

#include<iostream>
using namespace std;

int main()
{
   long int bin_one, bin_two, t1, t2;
   int i=0, rem=0, sum[16];
   cout<<"Enter First Binary Number: ";
   cin>>bin_one;
   cout<<"Enter Second Binary Number: ";
   cin>>bin_two;

   t1 = bin_one;
   t2 = bin_two;

   while(bin_one !=0 || bin_two !=0)
   {
      sum[i++] = (bin_one % 10 + bin_two % 10 + rem) % 2;
      rem = (bin_one % 10 + bin_two % 10 + rem) / 2;
      bin_one = bin_one/10;
      bin_two = bin_two/10;
   }
   
   if(rem!=0)
      sum[i++] = rem;

   i--;
   cout<<endl<<t1<<" + "<<t2<<" = ";

   while(i>=0)
      cout<<sum[i--];

   return 0;
}

Here is its sample run with user input: 101010 as the first and 110111 as the second binary number:

c++ program add binary numbers

In C++, add binary numbers using a user-defined function

Here is another program that does the same task as the previous two programs but uses a user-defined function named addBinNums() that takes two arguments. One for the first binary number entered by the user at run-time, and the other for the second binary number.

#include<iostream>
using namespace std;

int i=0, sum[16];
void addBinNums(int, int);
int main()
{
   long int bin_one, bin_two;
   cout<<"Enter First Binary Number: ";
   cin>>bin_one;
   cout<<"Enter Second Binary Number: ";
   cin>>bin_two;

   addBinNums(bin_one, bin_two);

   cout<<endl<<"Sum = ";
   while(i>=0)
      cout<<sum[i--];

   return 0;
}
void addBinNums(int b1, int b2)
{
   int r=0;
   while(b1 !=0 || b2 !=0)
   {
      sum[i++] = (b1 % 10 + b2 % 10 + r) % 2;
      r = (b1 % 10 + b2 % 10 + r) / 2;
      b1 = b1/10;
      b2 = b2/10;
   }
   if(r!=0)
      sum[i++] = r;
   i--;
}

Here is its sample run with user input, 110111 and 100011 as first and second binary numbers:

c++ binary number addition using function

In the above program, the statement int i=0, sum[16]; is declared globally, which is outside of both the main() and addBinNums() functions. So that we can use these two variables throughout the program along with their updated values.

C++ Quiz

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