递增递减运算符 ++ -- 前置后置的区别

1 

18 运算符-算术运算符-递增递减_哔哩哔哩_bilibili

2 .1

#include <iostream>
using namespace std;
int main() {

    int a = 0;
    int b = 0;

    a++ ;
    ++b ;

    cout << "a++ "  << a << endl;
    cout << "++b "  << b << endl;

}

2.2

#include <iostream>
using namespace std;
int main() {

    int a = 0;
    int b = 0;

    cout << "a++ "  << a++ << endl;
    cout << "++b "  << ++b << endl;
   
}

结论: 后置++ 本行变量使用旧值 下行变量值改变 (含有 a++行 值为旧值)
        前置++  值立马变

3 验证

#include <iostream>
using namespace std;
int main() {

    int a = 0;
    int b = 0;

    cout << "a++ "  << a++ << endl;
    cout << "++b "  << ++b << endl;
    cout << "a++ "  << a << endl;
   
}

4 a++ 复制给 变量b: 变量b是 a的旧值, a下行值改变

#include <iostream>
using namespace std;
int main() {

    int a = 0;
    int b = 0;
    b = a++ ;

    cout << "b "  << b << endl;
    cout << "a "  << a << endl;
    cout << "b "  << b << endl;
   
}