In C++, the “&” operator is known as the “address-of” operator. It is used to retrieve the memory address of a variable. This operator is particularly useful when dealing with pointers and passing variables by reference.

Here’s an example to illustrate the usage of the “&” operator:

#include <iostream>
using namespace std;

int main() {
  int num = 10;
  int* ptr = &num;

  cout << "Value of num: " << num << endl;
  cout << "Address of num: " << ptr << endl;

  return 0;
}

In the code above, we declare an integer variable num and assign it the value of 10. Then, we declare a pointer variable ptr and assign it the memory address of num. By using the “&” operator and prefixing it to the variable name (&num), we obtain the memory address of num and store it in ptr.

When we print num, it will display the actual value stored in the variable. However, when we print ptr, it will display the memory address where the variable num is stored.

The output of the above program would be:

Value of num: 10
Address of num: 0x7ffee8f585a8

In conclusion, the “&” operator in C++ allows us to obtain the memory address of a variable, enabling us to work with pointers and pass variables by reference.