C++中条件运算符？：作用在代码块的疑问

Question

我编写对成绩评级的代码，利用条件运算符，可是执行代码块部分却出现了问题，请指教!
编译错误提示：缺少“;”(在“{”的前面)
代码如下：
#include
#include
#include

using namespace std;

int main()
{
vector vec = { "E","D","C","B","A","A++" };
int grade;
string result;
cout << "请输入你的成绩：";
cin >> grade;
(grade < 0 || grade>100) ? {
cout << "该成绩不合法" << endl;
return -1;
}
: (grade < 60)
result = vec[0];
:
{
result = vec[(grade - 50) / 10];
if ((grade % 10) <= 3 && (grade % 10)>0)
result += '-';
else if ((grade % 10) >= 7)
result += '+';

}


cout << result << endl;
return 0;

}

Answer 1

你这个问题好有意思，我改了一下你的代码，大概弄出了这样的代码，不知道符不符合你的需求

 #include <iostream>
#include <vector>
#include "string"

using namespace std;

int getResult(string &result,int grade) {

    if ((grade % 10) <= 3 && (grade % 10)>0)
        result += '-';
    else if ((grade % 10) >= 7)
        result += '+';
    return 0;
}

int main()
{
    string vec[] = { "E","D","C","B","A","A++" };
    int grade;
    string result;
    cout << "请输入你的成绩：";
    cin >> grade;
    int b = (grade<0 || grade > 100)?(cout<<"该成绩不合法"<<endl,-1):
    (grade < 60?(result=vec[0],60)
     :(result = vec[(grade - 50) / 10],getResult(result,grade),100));

    if (b==-1) {
        return -1;
    }

    cout << result << endl;
    return 0;
}