C++ for with multiple control statements using comma operator

Question

How does comma operator if it is used in a 'for loop' for writing multiple control statements? i tried

#include <iostream>

using namespace std;

int main() {
        for (int x = 0, y = 0; x < 3, y < 4; ++x, ++y) {
                cout << x << " " << y << endl;
        }
        return 0;
}

and it seems like only the last expression is evaluated. Ty

comma operator here works the same as everywhere else: https://en.cppreference.com/w/cpp/language/operator_other — 463035818_is_not_an_ai, Jun 06 '20 at 14:13
Does this answer your question? [comma operator in if condition](https://stackoverflow.com/questions/16475032/comma-operator-in-if-condition) — cigien, Jun 06 '20 at 14:33

songyuanyao · Accepted Answer · 2020-06-06T15:05:06.243

5

This is how comma operator works. Its 1st operand x < 3 is evaluated, then the result is discarded; then the 2nd operand y < 4 is evaluated and the value is returned as the return value of the comma operator. x < 3 has not any effects here.

You might want to use operator&& or operator|| for this case, e.g. x < 3 && y < 4 or x < 3 || y < 4 based on your intent.

edited Jun 06 '20 at 15:05

answered Jun 06 '20 at 14:15

songyuanyao

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C++ for with multiple control statements using comma operator

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