Foreword

I encountered it when I was brushing the questions today, and I recorded it in a shallow way (maybe I don't know).In the C language, i++ and ++i both represent self-increment, the difference is that ++i is incremented first and then assigned, while i++ is incremented first.I think there are beginners like me who have been wondering before: they are both similar, so when to use i++ and when to use ++i?I just learned today that the judgment mechanism of i++ and ++i in the loop is different.

FOR loop

i++ and ++i are the same in the for loop, they are both judged first and then added.

for (int i = 0; i < 5; i++){cout << i << " ";}for (int i = 0; i < 5; ++i){cout << i << " ";}

The output is the same.

while loop

In the while loop, i++ and ++i are different: i++ is judged first, then incremented, and then entered into the loop body:

 int i = -5;while (i++ < 0){cout << i << " ";}

In the above code, first judge that i == -5 is less than zero, then increment i = i + 1, and finally enter the loop;

And ++i is to increase first, then judge and then enter the loop body:

 i = -5;while (++i < 0){cout << i << " ";}

In the above code, first increment i = i + 1, then judge that i == -4 is less than zero, and finally enter the loop;

The test results are as follows:

do-while loop

The i++ and ++i in the do-while loop are the same as in the while loop, except that the do-while executes the loop body first:

 cout << "do-while loop i++:";i = -5;do{cout << i << " ";} while (i++ < 0);cout << "do-while loop++i:";i = -5;do{cout << i << " ";} while (++i < 0);