C++ Precedence And Associativity

當你有算數的經驗時，你會知道在做四則運算時會有先乘除後加減的規則

程式當然也有，C++ 裡面也有相關的先後順序與關聯性

C++ Precedence and associativity

先前觀念

What is the purpose of {} in C++?

{} can be used to initialise variables in C++11 in the same way that they are used to initialise arrays and structures in C.

{} 可用於將C++ 已宣告的變數做 初始值代入。

範例01

#include <iostream>


int main(){

//初始值代入
    int a {6};
    int b {3};
    int c {8};
    int d {9};
    int e {3};
    int f {2};
    int g {5};
        
    int result = a + b * c -d/e -f + g; //  6 +  24  -   3 - 2 + 5
    
    std::cout << "result : " << result << std::endl;

    system("pause");

    return 0;
}

//結果:  6 +  24  -   3 - 2 + 5 = 30

範例02

#include <iostream>


int main(){

    int a {6};
    int b {3};
    int c {8};
    int d {9};
    int e {3};
    int f {2};
    int g {5};
        
    int result = a + b * c -d/e -f + g; //  6 +  24  -   3 - 2 + 5
    
    std::cout << "result : " << result << std::endl;

    result = a/b*c +d - e + f;  //   16 + 9 - 3 + 2
    std::cout << "result : " << result << std::endl;

    system("pause");

    return 0;
}

//結果:  6 +  24  -   3 - 2 + 5 = 30
//結果:   16 + 9 - 3 + 2 =24