C++中的i++与++i的区别的理解问题？

Question

C++教材有这样一道课后练习，通过观察两个人逐年的年龄变化让读者理解i++与++i的区别。练习题源代码如下：

#include<iostream>
using namespace std;
int main()
{
    int myAge=39;
    int yourAge=39;
    cout<<"I am: "<<myAge<<"years old."<<endl;
    cout<<"You are: "<<yourAge<<"years old."<<endl;
    myAge++;
    ++yourAge;
    cout<<"One year passes..."<<endl;
    cout<<"I am: "<<myAge<<"years old."<<endl;
    cout<<"You are: "<<yourAge<<"years old."<<endl;
    myAge++;
    ++yourAge;
    cout<<"Another year passes..."<<endl;
    cout<<"I am: "<<myAge++<<"years old."<<endl;
    cout<<"You are: "<<++yourAge<<"years old."<<endl;
    cout<<"Let's print it again."<<endl;
    cout<<"I am: "<<myAge<<"years old."<<endl;
    cout<<"You are: "<<yourAge<<"years old."<<endl;
    return 0;
}

如果是我自己手动算，最终的结果是如下：

I am: 39years old.
You are: 39years old.
One year passes...
I am: 40years old.
You are: 40years old.
Another year passes..
I am: 40years old.
You are: 41years old.
Let's print it again.
I am: 41years old.
You are: 41years old.

但是用dev编译器得到的运行结果如下：

I am: 39years old.
You are: 39years old.
One year passes...
I am: 40years old.
You are: 40years old.
Another year passes..
I am: 41years old.
You are: 42years old.
Let's print it again.
I am: 42years old.
You are: 42years old.

教材中有两句话是这样说的：

int i=1;
cout<<i++;           //首先使i自增为2，然后输出i自增前的值1
cout<<++i;           //首先使i自增为2，然后输出i的当前值2

请问是哪里出问题了呢？编译器会不会出错？（之前学C的时候就听说过不同编译器对自增自减这类运算有不同的运行结果）答案应该是什么样的呢？

Answer 1

前++，后++都是运算符，运算符说到底，就是一个函数，函数的功能具体要看实现，但大多时候有这样的约定，比如C/C++已经实现的这些操作（int和指针的++操作），i++一般是返回i自增前的值，++i是返回自增后的值，刚开始不懂你可以记一下，谁在左边，就先返回谁

你可以用下面的代码测试一下

#include <iostream>
using namespace std;
int pre(int& i) {       //i++;
    int t = i;
    //return post(i);
    i = i + 1;
    return t;       //返回增加前的值
}
int post( int& i) { //++i
    i = i + 1;
    return i;
}
int main() {
    int a = 1, b = 1;
    cout << a++ << pre(b) << endl;
    cout << ++a << post(b) << endl;
    return 0;
}