Unexpected result using ++ operation of C++

Asked Jun 02 '21 at 13:37

Active Jun 02 '21 at 13:37

Viewed 61 times

Good day guys, I'm a beginner of c++ and trying various approaches.

#include <iostream>

using namespace std;

int main() {
    int num = 0;
    while (num < 100) {
        cout << num << "\t" << num * num << "\n";
        num++;
    }
}

This code prints numbers and square numbers of these, as you know. And I wanted a minimalized version, so I tried it.

#include <iostream>

using namespace std;

int main() {
    int num = 0;
    while (num < 100) cout << num << "\t" << num * num++ << "\n";
}

But it prints

++n     n^2

unexpected. Why it results like this, and how to simplify it using the ++ operator properly? Thanks for reading.

asked Jun 02 '21 at 13:37

noError

This is undefined behavior. – Hatted Rooster Jun 02 '21 at 13:41
1

You have UB. `num * num++` is not properly defined. Also the operations on `cout << num << num++;` is considered UB prior to C++17 as order of the operations wasn't defined. – ALX23z Jun 02 '21 at 13:42
6

Your non-minimalized version is clean, tidy, readable, and above all, correct. Why change it? – acraig5075 Jun 02 '21 at 13:43
3

Change `while (num < 100)` to `for (int num = 0; num < 100; ++num)` and put the increment there. – Eljay Jun 02 '21 at 13:52
1

consider that code is written once but read many times. Hence trying to be too clever almost never pays off on the long run. – 463035818_is_not_an_ai Jun 02 '21 at 13:54

Unexpected result using ++ operation of C++

0 Answers0