SOURCE

var a=prompt("请输入你的成绩,我来告诉你等级");
num=parseInt(a/10);
switch(num){
    default:
    document.write("你不及格");
    break;
    case 10:
    case 9:
    document.write("优秀");
    break;
    case 8:
    document.write("良好");
    break;
    case 7:
    document.write("中等");
    break;
    case 6:
    document.write("及格");
    break;
    
}