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 else
23 {
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 else
36 {
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();
