算法竞赛入门经典第二章习题编程C#

string key = "y";
int i = 0;
string str;
while (key == "y")
{
do
{
Console.Write("请选择题号（1-10）：");
str = Console.ReadLine();
}
while ((!int.TryParse(str, out i)) || (i <= 0) || (i > 11));
switch (i)
{
case 1: digit(); break;
case 2: daffidil(); break;
case 3: hanxin(); break;
case 4: tringle(); break;
case 5: stat(); break;
case 6: harmony(); break;
case 7: approximation(); break;
case 8: subsequence(); break;
case 9: Decimal();break;
case 10: permutation();break;
case 11: s(); break;
}
Console.Write("是否继续（y/n）?");
key = Console.ReadLine();
}
}
public static int inputInt(string caption)
{
string str;
int n;
do
{
Console.Write("请输入" + caption + "(正整数)");
str = Console.ReadLine();
}
while ((!int.TryParse(str, out n)) || (n <= 0));
return n;
}
public static void digit()
{
Console.WriteLine("习题2-1 位数（digit）");
int n = inputInt("一个不超过1000000000的正整数");
int count = 0;
while (n > 0)
{
n = n / 10;
count++;
}
Console.WriteLine("{0}", count);
}
public static void daffidil()
{
Console.WriteLine("习题2-2 水仙花数（daffidil）");
int a, b, c;
for (int i = 100; i <= 999; i++)
{
a = i % 10; b = i / 10 % 10;
c = i / 100;
if (i == a * a * a + b * b * b + c * c * c)
Console.WriteLine("{0}", i);
}
}
public static void hanxin()
{
Console.WriteLine("习题2-3 韩信点兵（hanxin）");
int a = inputInt("第一个小于3的数");
int b = inputInt("第二个小于5的数");
int c = inputInt("第三个小于7的数");
for (int i = 10; i <= 100; i++)
{
if (i % 3 == a && i % 5 == b && i % 7 == c)
{
Console.WriteLine("{0}", i);
}
}
}
public static void tringle()
{
Console.WriteLine("习题2-4 倒三角形（tringle）");
int n = inputInt("n<=20的正整数");
for (int i = n; i >= 1; i--)
{