程序輸出（c ++的基本運算符）。 操作順序？

Question

// H2.cpp : Tihs program runs different mathmatical operations on numbers given by the user

#include <iostream>
#include <iomanip>
using namespace std;

int main()
{
    int a;
    cout << "Enter a number for a: "; //Prompts the user for a and b inputs
    cin >> a;

    int b;
    cout << "Enter a number for b: ";
    cin >> b;

    cout << "A is " << a << "\tB is " << b << endl;
    cout <<"Sum of a and b is equal to " << a << " + " << b << " and the result is " << (a + b) << endl; //Performs addition operator and gives output
    cout <<"Product of a and b is equal to " << a << " * " << b << " and the result is " << (a * b) << endl;
    cout <<"a > b is " << a << " > " << b << " and the result is " << (a > b) << endl;
    cout <<"a < b is " << a << " > " << b << " and the result is " << (a < b) << endl;
    cout <<"a == b is " << a << " == " << b << " and the result is " << (a == b) << endl; //Performs boolean operator and outputs result
    cout <<"a >= b is " << a << " >= " << b << " and the result is " << (a >= b) << endl;
    cout <<"a <= b is " << a << " <= " << b << " and the result is " << (a <= b) << endl;
    cout <<"a != b is " << a << " != " << b << " and the result is " << (a != b) << endl;
    cout <<"a -= b is " << a << " -= " << b << " and the result is a = " << (a -= b) << endl; //Performs - operator on a - b and makes a equal to the new result
    cout <<"a /= b is " << a << " /= " << b << " and the result is a = " << (a /= b) << endl;
    cout <<"a %= b is " << a << " %= " << b << " and the result is a = " << (a %= b) << endl; //Performs % operator on a % b and makes a equal to the new result. Ripple effect created from previous 2 lines as the value of a changes each time.

return 0;

我關注的輸出在這里：

a -= b is -4198672 -= 4198672 and the result is a = -4198672
a /= b is -1 /= 4198672 and the result is a = -1
a %= b is -1 %= 4198672 and the result is a = -1

似乎正在顯示的值是代碼行執行后的a值。 我確定這與操作順序有關，但是我不確定如何解決。 任何幫助是極大的贊賞。

Answer 1

在C ++中，未定義對運算符或函數的參數求值的順序。 如果對不同參數的求值有副作用，則只要編譯器認為合適，就會發生副作用，並且如果對同一對象進行多次修改，則結果將是不確定的行為。 如果要強制執行特定的求值順序，則需要將表達式分解為多個單獨的表達式，因為它們是按順序求值的，或者可以注入創建序列點的運算符。 但是，創建序列點的運算符不能很好地與鏈接輸出運算符配合使用。 強制在其他參數之前先求值第一個參數的運算符列表：

• 運營商
• 邏輯&&和|| 經營者
• 條件運算符？：

當然，如果您重載了這些運算符中的任何一個，當它們成為常規函數調用時，它們將停止引入序列點。

Answer 2

您列出的所有運算符都是比較運算符，它們返回值true或false。

除外：-=，/ =和％=運算符

a- = b實際上是a = ab。

只要檢查您是否確定首先要這樣做？

順便說一句：if（a = b）也總是返回true，因為它總是成功，但是我認為我們不是故意這樣做的。