C++ If Else 条件

Question

我已经尝试了很长时间，但似乎无法让它发挥作用。该程序不断引用每个输入值的第一个条件。有谁知道代码有什么问题吗？

#include <iostream>

using namespace std;

int main()
{
    int grade;

    cout <<"Enter a grade between 0 and 100:";
    cin>>grade;

    if (0 <= grade <= 59){
        cout<<"The grade for " <<grade<<" is  F";
    }
    else if (60 <= grade <= 69){
        cout<<"The grade for " <<grade<<" is  D";
    }
    else if (70 <= grade <= 79){
        cout<<"The grade for " <<grade<<" is  C";
    }
    else if (80 <= grade <= 89){
        cout<<"The grade for " <<grade<<" is  B";
    }
    else if (90 <= grade <= 100){
        cout<<"The grade for " <<grade<<" is  A";
    }
    system("pause");
    return 0;
}

Answer 1

重写守卫

0 <= grade <= 59

与

0 <= grade && grade <= 59

C++ 像这样解析你的表达式:

(0 <= grade) <= 59

因此它将 bool 值与 59 进行比较。也就是说， bool 值 true 为 1，并且第一个 if block 被触发