答案(两种)

#include <iostream>

 using namespace std; 

int main() { 

int score; 

cin >> score;

 if (score >= 90) { 

cout << "A" << endl; 

} else if (score >= 70) { 

cout << "B" << endl; 

} else if (score >= 60) {

 cout << "C" << endl; 

} else { 

cout << "D" << endl;

 } 

return 0; 

}

#include <iostream>

 using namespace std; 

int main() { 

int score;

 cin >> score; 

 int tens = score / 10;

 switch(tens) { 

case 9: 

 cout << "A" << endl; 

break; 

case 7: 

 case 8: 

 cout << "B" << endl;

 break;

case 6: 

 cout << "C" << endl; 

break;

 default:

 cout << "D" << endl;

 break; 

} 

return 0;

 }