与公式相关的代码片段

前段时间，一同事写得代码惨不忍睹，核心是自定义公式，他的实现方式是“纯手工”打造...

以下代码仅作参考：

class Express
    {
        DataTable TmpDt;
        public Express()
        {
            TmpDt =new DataTable();
            TmpDt.Columns.Add("f1", typeof(double));
            TmpDt.Columns.Add("f2", typeof(double));
            TmpDt.Columns.Add("f3", typeof(double));

            DataRow dr =TmpDt.NewRow();
            dr["f1"]=5;
            dr["f2"]=3;
            dr["f3"]=1;
            TmpDt.Rows.Add(dr);

            DataRow dr1 =TmpDt.NewRow();
            dr1["f1"] =15;
            dr1["f2"] =13;
            dr1["f3"] = DBNull.Value;
            TmpDt.Rows.Add(dr1);
        }

        publicstring test()
        {
            return TmpDt.Columns["f1"].Expression ="f2*f3";//将第二列与第三列 相乘
        }

        publicobject test(int i)
        {
            object objTmp=null;
            switch(i)
            {
                case1:
                    objTmp = TmpDt.Compute("Count(f1)", "f1=5");
                    break;
                case2:
                    objTmp = TmpDt.Compute("1=2", "");
                    break;
                case3:
                    objTmp = TmpDt.Compute("5+30", "");
                    break;
                case4:
                    objTmp = TmpDt.Compute("IIF(2000>1000, null, 1)","");
                    break;
                case5:
                    objTmp = TmpDt.Compute("IsNull(null,0)", "");
                    break;
                case6:
                    objTmp = TmpDt.Compute("Trim('1235      ')", "");
                    break;
                case7:
                    objTmp = TmpDt.Compute("SubString('1235',1,2)", "");//从1开始
break;
                case8:
                    objTmp = TmpDt.Compute("IsNull(IIF(2000>1000, null, 1),5)", "");//允许嵌套
break;
                default:
                    break;

            }
            return objTmp;
        }

        publicdouble? test12(int i)
        {
            double? _value=null;
            var employees =new List<Employess>
            {
                new Employess{ Salary=123},
                new Employess{Salary=234},
                new Employess{Salary=null}
            };
            switch (i)
            {
                case1:
                    _value = employees.Sum(c => c.Salary);
                    break;
                case2:
                    _value = employees.Average(c => c.Salary);
                    break;
                case3:
                    _value = employees.Min(c => c.Salary);
                    break;
                case4:
                    _value = employees.Max(c => c.Salary);
                    break;
                case5:
                    _value = employees.Select(c => c.Salary).Aggregate((x, y) => x * y);
                    break;
                default:
                    break;
            }
            return _value;
        }

    }

    publicsealedclass Employess
    {
        privatedouble? salary;

        publicdouble? Salary
        {
            get { return salary; }
            set { salary = value; }
        }

        
    }

class Program
    {
        staticvoid Main(string[] args)
        {
            DataTable dt =new DataTable();
           //A:
try
            {
                Console.WriteLine(dt.Compute(Console.ReadLine(), ""));
            }
            catch(Exception en)
            {
                Console.WriteLine(en.Message);
            }
            //goto A;

            Express ex =new Express();
            //Console.WriteLine(ex.test(3));
            //ex.test();
            Console.WriteLine(ex.test12(5));
 
            int[] nums =newint[] { 10, 20, 30, 40, 50 };
            int sum1 = nums.Where((n, i) => i %2==0).Sum();//Where用法  10 + 30 + 50
            Console.WriteLine(sum1);

            //取款问题
double startBalance =100.0;
            int[] test3 = { 20, 10, 40, 50, 10, 70, 30 };
            double endBalance = test3.Aggregate(startBalance,
                (balance, nextWithdrawal) =>
                        ((nextWithdrawal <= balance) ? (balance - nextWithdrawal) : balance));
            Console.WriteLine(endBalance);


            //1~n放在含有n+1个元素的数组中，只有唯一的一个元素值重复，最简算法找出重复的数  o(╯□╰)o暂时不懂神马意思
int[] array =newint[] { 8,1,1,1,5 };
            int repeatedNum1 = array.Select((i, j) => i - j).Sum();
            Console.WriteLine(repeatedNum1);//Select用法


            List<double> lst =new List<double>();
            lst.AddRange(newdouble[] {1.1,1.123123
                                    });
            Console.WriteLine(lst.Aggregate((total, next) => total * next));


            string[] words =newstring[] { "Able", "was", "I", "ere", "I", "saw", "Elba" };
            string normal = words.Aggregate((a, n) => a +""+ n);
            Console.WriteLine("正常："+ normal);

            //sql 中 in 
            StringBuilder sb =new StringBuilder() ;  
            words.Aggregate<string, StringBuilder>(sb, (sbobj, str) => sbobj.Append("'"+str).Append("',"));
            Console.WriteLine(sb.ToString());
        }
    }