选择语句（条件语句）： 1、 if   if...else   if...else if...else  2、 switch  case 1  case 2 ... case n   default  1 //case 1：成绩 2             Console.Write("请输入姓名："); 3             Console.ReadLine(); 4             Console.WriteLine("请输入分数："); 5             double a = double.Parse(Console.ReadLine()); 6             if(a>=80 && a<=100) 7             { 8                 Console.WriteLine("学得不错，值得表扬！"); 9             }10             if (a >= 60 && a < 80)11             {12                 Console.WriteLine("还不错，再加把劲！");13             }14             if (a >= 50 && a < 60)15             {16                 Console.WriteLine("就差一点点，再加把劲！");17             }18             if (a >= 0 && a < 50)19             {20                 Console.WriteLine("使劲努力，不要偷懒！");21             }22             else23             {24                 Console.WriteLine("您的输入有误");25             }26             Console.ReadLine();

1 //case 2:标准体重 2             Console.Write("请输入性别："); 3             string s = Console.ReadLine(); 4             Console.Write("请输入体重："); 5             double w = double.Parse(Console.ReadLine()); 6             Console.Write("请输入身高："); 7             double h = double.Parse(Console.ReadLine()); 8             if(s=="男") 9             {10                 double m = w - h + 100;11                 if(m>=-3 && m<=3)12                 {13                     Console.WriteLine("您的体重是标准体重！");14                 }15                 else if (m > 3)16                 { 17                     Console.WriteLine("您需要减肥了！");18                 }19                 else 20                 {21                     Console.WriteLine("您需要补充营养！");22                 }23             }24             else if (s == "女")25             {26                 double f = w - h + 110;27                 if (f >= -3 && f <= 3)28                 {29                     Console.WriteLine("您的体重是标准体重！");30                 }31                 if (f > 3)32                 {33                     Console.WriteLine("您需要减肥了！");34                 }35                 else36                 {37                     Console.WriteLine("您需要补充营养！");38                 }39             }40             else 41             {42                 Console.WriteLine("您的输入有误！");43             }44             Console.ReadLine();

1  //case 3:月份 2             int m1 = 31, m2 = 28, m3 = 31, m4 = 30, m5 = 31, m6 = 30, 3                 m7 = 31, m8 = 31, m9 = 30, m10 = 31, m11 = 30; 4             Console.WriteLine("请输入月份："); 5             int mm = int.Parse(Console.ReadLine()); 6             Console.WriteLine("请输入日期："); 7             int d = int.Parse(Console.ReadLine()); 8             switch(mm) 9             {10             case 1:11                 Console.WriteLine("第"+d+"天");12                 break;13             case 2:14                 Console.WriteLine("第"+(d+m1).ToString()+"天");15                 break;16             case 3:17                 Console.WriteLine("第"+(d+m1+m2).ToString()+"天");18                 break;19             case 4:20                 Console.WriteLine("第"+(d+m1+m2+m3).ToString()+"天");21                 break;22             case 5:23                 Console.WriteLine("第"+(d+m1+m2+m3+m4).ToString()+"天");24                 break;25             case 6:26                 Console.WriteLine("第"+(d+m1+m2+m3+m4+m5).ToString()+"天");27                 break;28             case 7:29                 Console.WriteLine("第"+(d+m1+m2+m3+m4+m5+m6).ToString()+"天");30                 break;31             case 8:32                 Console.WriteLine("第"+(d+m1+m2+m3+m4+m5+m6+m7).ToString()+"天");33                 break;34             case 9:35                 Console.WriteLine("第"+(d+m1+m2+m3+m4+m5+m6+m7+m8).ToString()+"天");36                 break;37             case 10:38                 Console.WriteLine("第"+(d+m1+m2+m3+m4+m5+m6+m7+m8+m9).ToString()+"天");39                 break;40             case 11:41                 Console.WriteLine("第"+(d+m1+m2+m3+m4+m5+m6+m7+m8+m9+m10).ToString()+"天");42                 break;43             case 44                 12:45                 Console.WriteLine("第"+(d+m1+m2+m3+m4+m5+m6+m7+m8+m9+m10+m11).ToString()+"天");46                 break;47             default:48                 Console.WriteLine("您的输入有误");49                 break;50             }51             Console.ReadLine();