Practical C Programming, 3rd Edition

The comma operator (,) can be used to group statements. For example:

if (total < 0) { std::cout << "You owe nothing\n"; total = 0; }

can be written as:

if (total < 0) std::cout << "You owe nothing\n", total = 0;

In most cases, { } should be used instead of a comma. About the only place the comma operator is useful is in a for statement. The following for loop increments two counters, two and three , by 2 and 3:

for (two = 0, three = 0; two < 10; two += 2, three += 3) std::cout << two << ' ' << three << '\n';