一。while 循环

while(循环的判断条件）如果条件为真就会一直执行循环体中的内容 { 循环体 } //死循环 判断条件一直为真 //有限循环 只需要让判断条件有一天变 为假 //i=1 i<10 => i++ 有一天i就会大于等于10 增量表达式

namespace demo2
{
    class Programs
    {
        static void Main(string[] args)
        {
            while (true)
            {
                Console.WriteLine(1);
            }
        }
    }
}

                 Console.WriteLine("输入一个n");
                 int n = Convert.ToInt32(Console.ReadLine());
                 int i = 1;
                 while (i<=n)
                 {
                     A +=i;
                    
                     Console.WriteLine(A);
                i++;
                 }

                int n = Convert.ToInt32(Console.ReadLine());
                int a = 0;
                while(n!=1)
                {
                    if(n%2==0)
                    {
                        n = n / 2; 
                    }
                    else
                    {
                        n = 3 * n + 1;  
                    }
                    a++;
                }
                Console.WriteLine(a);

                int n = Convert.ToInt32(Console.ReadLine());
                int i = 1;
                int sum = 0;
                double B;
                while (i<=n)
                {
                    Console.WriteLine("输入年龄");
                    i++;
                    int a = Convert.ToInt32(Console.ReadLine());
                    sum = sum + a;
                }
                B = sum / n;
                Console.WriteLine(Math.Round(B, 2));

二、for循环

for(初始化；判断条件；增量表达式） { 循环体 }

                 int n = Convert.ToInt32(Console.ReadLine());
                 int m = Convert.ToInt32(Console.ReadLine());
                 int sum;
                 sum = 0;
                 int num1 = n;
                 if(n>num1)
                 {
                     n = m;
                     m = num1;
                 }
                 for (; n <= m; n++)
                 {
                     if(n%17==0)
                     {
                         sum = sum + n;
                     }
                 }
                 Console.WriteLine(sum);

                 int a = Convert.ToInt32(Console.ReadLine());
                 int n = Convert.ToInt32(Console.ReadLine());
                 int C=1;
                 for(int i = 1;i<=n;i++)
                 {
                     C *= a;                  
                 }               
                 Console.WriteLine(C);

                 double height = Convert.ToDouble(Console.ReadLine());
                 int i = 1;
                 double sum = 0;
                 for(;i<=10;i++)
                 {
                     sum = sum + height;
                     height /= 2;
                     sum += height;
                 }
                 Console.WriteLine(sum);

                int a, b, c, A;
                for(;i<=999;i++)
                {
                    a = i / 100;
                    b = i % 100 / 10;
                    c = i % 100 % 10;
                    A = a * a * a + b * b * b + c * c * c;
                    if (i == A)
                    {
                        Console.WriteLine(i);
                    }
                }

三、do...while 循环 先执行，do中语句然后再循环

                do//不管后面的while循环的条件满不满足都会先执行一次
                {
                    Console.WriteLine(num1);
                    num1++;
                }
                while (num1 < 10);
                Console.WriteLine(num1);

四、break continue

break 跳出整个循环

continue 跳出当前这一次