## Program to find two’s complement of a binary number in C++

**Problem – **Binary Number as a string, we have to print its 2’s complement.

**2’s complement of a binary number is another binary number obtained by adding 1 to one’s complement.**

**Example:**

**Input:** 101010

One’s complement the number: 010110

**Algorithm:**

- Take binary number input as string having length say size.
- Initialise int fail=0.
- Start loop from i=0 to i<size

if binary[i]==1

then one[i]=0

else if binary[i]==0

then one[i]=1

else

print “error! Enter binary number of assigned size”

fail=1

break - Put null character in the string complement

one[size] = ‘\0’ - If fail ==0 then print the ones complement.
- Start loop from i = size – 1 to i >= 0.

if (one[i] == ‘1’ && carry == 1)

two[i] = ‘0’;

else if (one[i] == ‘0’ && carry == 1)

two[i] = ‘1’;

carry = 0;

else

two[i] = one[i]; - Put null character in the string two.

two[size] = ‘\0’; - if fail == 0

then print two’s complement.

**Code:**

```
//Program to find two's complement of a binary number
#include <iostream>
#define size 6
using namespace std;
int main() {
char binary[size + 1], one[size + 1], two[size + 1];
int i, carry = 1, fail = 0;
cout << " Input a " << size << " bit binary number: ";
cin >> binary;
for (i = 0; i < size; i++) {
if (binary[i] == '1') {
one[i] = '0';
} else if (binary[i] == '0') {
one[i] = '1';
} else {
cout << "Error! Input the number of assigned bits." << endl;
fail = 1;
break;
}
}
one[size] = '\0';
for (i = size - 1; i >= 0; i--) {
if (one[i] == '1' && carry == 1) {
two[i] = '0';
} else if (one[i] == '0' && carry == 1) {
two[i] = '1';
carry = 0;
} else {
two[i] = one[i];
}
}
two[size] = '\0';
if (fail == 0) {
cout << " The original binary = " << binary << endl;
cout << " After ones complement the value = " << one << endl;
cout << " After twos complement the value = " << two << endl;
}
}
```

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