C++ C++；如果其他条件

我已经试了这么长时间，但我似乎无法让它发挥作用。程序不断引用每个输入值的第一个条件。有人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;
}

#包括
使用名称空间std；
int main（）
{
国际等级；
cout分级；
如果（0重写

0 <= grade <= 59

0您不能写入
0您在检查范围条件时出错了。
测量范围的正确方法是使用
&&
运算符

这样做：

(0 <= grade) <= 59

if (grade>=0 && grade <= 59)  // it means grade is greater or equal to 0 and grade is lesser or equal to 59 

如果（grade>=0&&grade谢谢你在旁注中的帮助，请看。
if (grade>=0 && grade <= 59)  // it means grade is greater or equal to 0 and grade is lesser or equal to 59