为什么 cout 和 return 在以下 C++ 代码中给出不同的值？

Question

#include <iostream>

using namespace std;

int fn1 (){
    int a = 5;
    int b = 6;
    cout << (++a > b--)? (a+b):(a-b) ;
    a = 5;
    b = 6;
    return (++a > b--)? (a+b):(a-b);
}

int main (){
    cout << fn1();
}

// Output: 01

Answer 1

Operator precedence.

cout << (++a > b--)? (a+b):(a-b);

is parsed as:

(cout << (++a > b--))? (a+b):(a-b);

which first evaluates the cout << then the rest.