How to use extern in C? / C ++Why do we exchange the values of two variables without using a third variable in C?

Below is an example of adding two numbers without using arithmetic operators.

Example

#include <iostream>
#include <cmath>
using namespace std;
int add(int val1, int val2) {
　　　while(val2　!= 0) {
　　　　　　int c = val1　& val2;
　　　　　　val1　= val1　^ val2;
　　　　　　val2　= c <<　1;
　　　}
　　　return val1;
}
int main() {
　　　cout << "The sum of two numbers: " << add(28,　8);
　　　return 0;
}

Output result

The sum of two numbers:　36

In the above program, the function add() defines two int type parameters. The addition of two numbers is encoded in the add() function

int add(int val1, int val2) {
　　　while(val2　!= 0) {
　　　　　　int c = val1　& val2;
　　　　　　val1　= val1　^ val2;
　　　　　　val2　= c <<　1;
　　　}
　　　return val1;
}

Print the result by calling the function add() in the main() function

cout << "The sum of two numbers: " << add(28,　8);