切换语句c帮助

#include <iostream>

using namespace std;

int main()
{
    int score;
char grade;
cout << "Enter your score:" << endl;
cin >> score;
if (score >= 90)
    grade = 'a';
if (score >= 80)
    grade = 'b';
if (score >= 70)
    grade = 'c';
if (score >= 60)
    grade = 'd';
else 
    grade = 'f';
cout << grade << endl;
switch (grade) {
    case 'a':
        cout << "Good job" << endl;
        break;
    case 'c':
        cout << "Fair job" << endl;
        break;
    case 'f':
        cout << "Failure" << endl;
        break;
    default:
        cout << "invalid" << endl;
}
cin.get();
return 0;
  }

当我输入95时,为什么它会给我我的默认开关案例,当我应该得到案例a