1. 给出一个百分制成绩，要求输出成绩等级A、B、C、D和E。90分以上为A，89～80为B，79～70为C，69～60为D

#include
using namespace std;

void main(){
cout<<"请输入成绩";
int score;
cin>>score;
while(score<0||score>100){
cout<<"您输入的成绩不符合要求，请重新输入";
cin>>score;
}
switch(score/10){
case 10:
case 9:
cout<<"A";
break;
case 8:
cout<<"B";
break;
case 7:
cout<<"C";
break;
case 6:
cout<<"D";
break;
default:
cout<<"E";
}
system("pause");
}

这种情况是标准的使用switch的情况，用if也行，更简单：
#include
using namespace std;

void main(){
cout<<"请输入成绩";
int score;
cin>>score;
while(score<0||score>100){
cout<<"您输入的成绩不符合要求，请重新输入";
cin>>score;
}
if(score>=90){
cout<<"A";
}else{
if(score>=80){
cout<<"B";
}else{
if(score>=70){
cout<<"C";
}else{
if(score>=60){
cout<<"D";
}else{
cout<<"E";
}
}

}
}
system("pause");
}