What is the built-in comma operator in C++?

The comma operator evaluates all of its operands from left to right and returns the value of the last one.

#include <iostream>
int main() {
  int n = 1;
  int m = (
    ++n, // n = n + 1 = 1 + 1 = 2
    std::cout << "n = " << n << '\n', // Displays "n = 2"
    ++n, // n = n + 1 = 2 + 1 = 3
    2 * n // 2 * 3 = 6
  ); // The operands are executed sequentially,
     // the result of the last expression is assigned
     // to a variable: 2 * n = 2 * 3 = 6
  std::cout << (++m, m); // First operand evaluates
                         // and its result is discarded,
                         // expression evaluates to
                         // 7
}

What is the built-in comma operator in C++?

Syntax

Code