Subtraction of two numbers using 2’s Complement

Given two numbers a and b. The task is to subtract b from a by using 2’s Complement method.

Note: Negative numbers represented as 2’s Complement of Positive Numbers.

For example, -5 can be represented in binary form as 2’s Compliment of 5. Look at the image below:



Examples:

Input : a = 2, b = 3
Output : -1

Input : a = 9, b = 7
Output : 2

To subtract b from a. Write the expression (a-b) as:

(a - b) = a + (-b)

Now (-b) can be written as (2’s complement of b). So the above expression can be now written as:

(a - b) = a + (2's complement of b)

So, the problem now reduces to “Add a to the 2’s complement of b“. Below image illustrates the above method of subtraction for the first example where a = 2 and b = 3.

Below is the implementation of above method:

C++

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#include <bits/stdc++.h>
using namespace std;
  
// function to subtract two values
// using 2's complement method
int Subtract(int a, int b)
{
    int c;
  
    // ~b is the 1's Complement of b 
    // adding 1 to it make it 2's Complement
    c = a + (~b + 1);
  
    return c;
}
  
// Driver code
int main()
{
    int a = 2, b = 3;
  
    cout << Subtract(a, b)<<endl;
  
    a = 9; b = 7;
    cout << Subtract(a, b);
  
    return 0;
}

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Java














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class GFG  


{ 


  


// function to subtract two values 


// using 2's complement method 


static int Subtract(int a, int b) 


{ 


    int c; 


  


    // ~b is the 1's Complement 


    // of b adding 1 to it make  


    // it 2's Complement 


    c = a + (~b + 1); 


  


    return c; 


} 


  


// Driver code 


public static void main(String[] args) 


{ 


    int a = 2, b = 3; 


      


    System.out.println(Subtract(a, b)); 


      


    a = 9; b = 7; 


    System.out.println(Subtract(a, b)); 


} 


} 


  


// This code is contributed  


// by ChitraNayal 



















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Python3














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# python3 program of subtraction of 


# two numbers using 2's complement . 


  


# function to subtract two values 


# using 2's complement method 


def Subtract(a,b): 


      


    # ~b is the 1's Complement of b  


    # adding 1 to it make it 2's Complement 


    c = a + (~b + 1) 


    return c 


  


# Driver code 


if __name__ == "__main__" : 


  


    # multiple assignments 


    a,b = 2,3


    print(Subtract(a,b)) 


  


    a,b = 9,7


    print(Subtract(a,b)) 



















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C#














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// C# program of subtraction of 


// two numbers using 2's complement 


using System; 


  


class GFG 


{ 


// function to subtract two values 


// using 2's complement method 


static int Subtract(int a, int b) 


{ 


    int c; 


  


    // ~b is the 1's Complement 


    // of b adding 1 to it make  


    // it 2's Complement 


    c = a + (~b + 1); 


  


    return c; 


} 


  


// Driver code 


static void Main() 


{ 


    int a = 2, b = 3; 


      


    Console.WriteLine(Subtract(a, b)); 


      


    a = 9; b = 7; 


    Console.WriteLine(Subtract(a, b)); 


} 


} 


  


// This code is contributed  


// by mits 



















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PHP














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<?php 


// function to subtract two values 


// using 2's complement method 


function Subtract($a, $b) 


{ 


  


    // ~b is the 1's Complement  


    // of b adding 1 to it make  


    // it 2's Complement 


    $c = $a + (~$b + 1); 


  


    return $c; 


} 


  


// Driver code 


$a = 2; 


$b = 3; 


  


echo Subtract($a, $b) . "\n"; 


  


$a = 9; 


$b = 7; 


echo Subtract($a, $b) . "\n"; 


  


// This code is contributed  


// by ChitraNayal 


?> 



















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Output:


-1
2




          
          
          
          

            

    

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