C++编译正常，调试出现Debug Error（见图）

#include <iostream>
using namespace std;
int main()
{
    float score;
    char grade;
    cout <<"请输入学生成绩"<<'\n';
    cin >>score;
    while (score>100||score<0)
    {
        cout <<"请重新输入"<<'\n';
        cin >>score;

    }
    switch (grade)
    {
    case'A':cout<<"90~100\n";
    case'B':cout<<"80~89\n";
    case 'C':cout<<"70~79\n";
    case 'D':cout<<"60~69\n";
    case'E':cout<<"<60\n";
    default:cout<<"error\n";
        break;
    }
    cout << "score is"<<score<<",grade is"<<grade<<endl;
    return 0;
}

调试出现下面情况

你的代码很奇怪，一个是输入成绩，一个是输入字母的成绩，你要两者选其一
要么输入等级，输出成绩的范围
char grade = '\0';
cout << "请输入等级ABCDE";
cin >> grade;

或者输入成绩后，程序得到grade
if (score >= 90 && score <= 100)
grade = 'A';
else if (score >= 80 && score <= 89)
grade = 'B';
...