Add Two Numbers in C++

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Given two integers, the task is to add these integer number and print their sum in C++.

Examples

Input: a = 11, b = 9
Output: 20
Explanation: Sum of 11 + 9 = 20

Input: a = 1, b = 8
Output: 9
Explanation: Sum of 1 + 8 = 9

Add Two Numbers Using Addition Operator

In C++, the simplest method for adding the two numbers is using the addition operator(+). This operator adds the given two values and return their sum.

Code Implementation

// C++ program to add two number using
// addition operator
#include <bits/stdc++.h>
using namespace std;

int main() {
    int a = 11, b = 9;

    // Adding the two numbers and printing
    // their sum
    cout << a + b;
    return 0;
}

20

Time Complexity: O(1)
Auxiliary Space: O(1)

Other Methods for Adding Two Numbers in C++

Apart from addition operator, there are also the various methods by which we can add two integers.

Using Increment Operator (++)

We can also add two numbers in C++ using the increment operator by repeatedly increasing the first value to the number of times equal to second value using a loop.

Code Implementation

// C++ Program to add two numbers using
// increment operator
#include <bits/stdc++.h>
using namespace std;

int main() {
    int a = 11, b = 9;

    // If b is positive, increment a to b times
    for (int i = 0; i < b; i++)
        a++;

    // If b is negative, decrement a to |b| times
    for (int i = 0; i > b; i--)
        a--;

    cout << a;

    return 0;
}

20

Time Complexity: O(b), where b is the second number
Auxiliary Space: O(1)

Using Bitwise Operators

According to the Half Adder logic, sum of two bits can be obtained by using Bitwise XOR(^) and carry bit can be obtained by performing Bitwise AND(&) of two bits. We can extend this logic to integers that contains multiple bits.

Approach

• Read two integers from the user.
• Use the bitwise XOR (^) operator to add the numbers without considering the carry.
• Use the bitwise AND (&) operator to calculate the carry.
• Left shift the carry by one position to align it for the next bit addition.
• Repeat the process until there is no carry left.

Code Implementation

// C++ program to add two numbers by using
// Bitwise operator or Half Adder Method
#include <bits/stdc++.h>
using namespace std;

int main() {
    int a = 11, b = 9, carry;

    while (b) {

        // Carry is AND of a and b
        carry = a & b;

        // Sum without carry is XOR of a and b
        a = a ^ b;

        // Carry is shifted by one so that it can be
        // added in the next iteration
        b = carry << 1;
    }

    cout << a;
    return 0;
}

20

Time Complexity: O(log b), where b is the second number.
Auxiliary Space: O(1)