double dbA; string strA; Console.WriteLine(" 学生成绩管理系统"); Console.WriteLine(" 输入(-1退出系统)"); do { Console.Write("请输入学生的成绩:"); dbA = Convert.ToDouble(Console.ReadLine()); if (dbA == -1) { break; } if (dbA < 0 || dbA > 100) { Console.WriteLine("您输入的成绩不合法请重新输入"); continue; } switch ((int)(dbA / 10)) { case 10: case 9: strA = "优秀"; break; case 8: strA = "良"; break; case 7: strA = "中"; break; case 6: strA = "及格"; break; default: strA = "不及格"; break; } Console.WriteLine(strA); strA = ""; dbA = 0; } while (true); Console.WriteLine("感谢使用!"); Console.ReadLine();