认识 Linq
List<Student> Students = new StudentDbProvider().StudentOperation.Get().ToList(); List<StudentScore> csScores = new StudentDbProvider().StudentScoreOperation.Get("C#").ToList(); List<StudentScore> dbScores = new StudentDbProvider().StudentScoreOperation.Get("DB").ToList(); //查询查询课程总分和平均分 ---非Linq方式 int csScoreSum = 0; int dbScoreSum = 0; double csScoreAvg = 0.0; double dbScoreAvg = 0.0; foreach (StudentScore csScore in csScores) { csScoreSum += Convert.ToInt32(csScore.Score); } foreach (StudentScore dbScore in dbScores) { dbScoreSum += Convert.ToInt32(dbScore.Score); } csScoreAvg = csScoreSum / Students.Count(); dbScoreAvg = dbScoreSum / Students.Count(); Console.WriteLine("C#课程分总和:" + csScoreSum + "平均分:" + csScoreAvg); Console.WriteLine("DB课程分总和:" + dbScoreSum + "平均分:" + dbScoreAvg); Console.ReadLine(); //查询查询课程总分和平均分 ---Linq方式 Console.WriteLine("C#课程分总和:{0}平均分:{1}", csScores.Sum(c=>c.Score),csScores.Average(c=>c.Score)); Console.WriteLine("DB课程分总和:{0}平均分:{1}", dbScores.Sum(c => c.Score), dbScores.Average(c => c.Score)); Console.ReadLine(); //根据学生查询各学科的总分和平均分 ---非Linq方式 List<StudentScoreReport> Reports = new List<StudentScoreReport>(); foreach (Student student in Students) { StudentScoreReport report = new StudentScoreReport(); report.StudentId = student.Id; report.Name = student.Name; foreach (StudentScore csScore in csScores) { if (csScore.Id == student.Id) { report.ScoreSum += csScore.Score; break; } } foreach (StudentScore dbScore in dbScores) { if (dbScore.Id == student.Id) { report.ScoreSum += dbScore.Score; break; } } report.ScoreAvg = report.ScoreSum / 2; Reports.Add(report); } foreach (StudentScoreReport report in Reports) { Console.WriteLine("学生:{0} 的总分:{1},平均分:{2}", report.Name, report.ScoreSum, report.ScoreAvg); } Console.ReadLine(); //根据学生查询各学科的总分和平均分 ---Linq方式 var studentScoreQuery = from student in Students join csScore in csScores on student.Id equals csScore.Id join dbScore in dbScores on student.Id equals dbScore.Id select new { ID = student.Id, Name = student.Name, ScoreSum = csScore.Score + dbScore.Score, ScoreAvg = (csScore.Score + dbScore.Score) / 2 }; foreach (var studentScore in studentScoreQuery) { Console.WriteLine("学生:{0} 的总分:{1},平均分:{2}", studentScore.Name, studentScore.ScoreSum, studentScore.ScoreAvg); } Console.ReadLine(); //扩展类 int Money=123456789; double p = 0.1029; Console.WriteLine(Money.FormatMoney()); Console.WriteLine(p.FormatPercent()); Console.ReadLine();