How does the Comma Operator work in C++

The purpose of comma operator is to combine several expressions. The value of a comma-separated list of expressions is the value of the right-most expression. Comma's effect is to allow a sequence of operations to be performed.

The values of the other expressions are discarded, which means that the expression on the right side will become the value of the entire comma-separated expression.

example

The following program illustrates the working of comma operator −

#include <iostream>
using namespace std;
int main() {
   int i, j;
   j = 10;
   i = (j++, j+100, 999+j);
   cout << i;
   return 0;
}

Output

This gives the output −

1010

Here is the procedure how the value of i gets calculated: j starts with the value 10. j is then incremented to 11. Next, j is added to 100. Finally, j (still containing 11) is added to 999, which yields the result 1010.