C#入门第五课循环结构

循环结构

while循环结构

while(条件表达式)
{
}
条件表达为真，执行循环体，一旦表达式为假，循环停止。
例如：

int num1 = 0;
            int a = 100;
            while (a <= 10000)
            {
                int a1 = a % 10;
                int a2 = a / 10 % 10;
                int a3 = a / 10 / 10 % 10;
                int a4 = a / 10 / 10 / 10 % 10;
                int a5 = a / 10 / 10 / 10 / 10 % 10;
                int q = a1 + a2 + a3 + a4 + a5;
                if (q == 7)
                {
                    num1 += 1;
                }
                a += 1;
            }
            Console.WriteLine(num1);
            int b = 1;
            int num2 = 0;
            while (b <= 100)
            {
                b += 1;
                if (b % 2 == 0)
                {
                    Console.Write(b+" ");
                }
            }
            Console.WriteLine();
            int c = 1;
            int num3 = 0;
            while (c <= 100)
            {               
                num3 = num3 + c;
                c += 1;
            }
            Console.WriteLine(num3);

break
switch语句中跳出switch语句
循环体中用来跳出循环（通常与if一起用）

int a = 8;
            int b = new Random().Next(100, 300);
            while (true)
            {
                int c = new Random().Next(a - 2, a + 3);
                b -= c;
                Console.WriteLine("敌人受到了" + c + "点伤害");
                if (b <= 0)
                {
                    break;
                }
            }

while (true)
            {
                int a = Convert.ToInt32(Console.ReadLine());
                if (a < 0)
                {
                    Console.WriteLine("结束");
                    break;
                }
            }

continue
在循环中的作用：结束本次循环，后面的代码不再执行，进入下一次循环（通常与if连用）

int a = 1;
            while (a <= 100)
            {

                if (a % 3 == 0)
                {
                    a++;
                    continue;
                }
                Console.WriteLine(a);
                a++;
            }

do while循环

不常用，先执行循环体，再判断循环条件，直到条件不满足时候，循环结束。

int sum = 0;
            int a = 1;
            do
            {
                sum = sum + a;
                a++;
            }
            while (sum <= 10000);
            Console.WriteLine(sum-a);
            Console.WriteLine(a-1);

for循环

for(循环变量初始化；循环条件；循环增量)
{
}
循环条件为真，执行循环体。
循环条件为假，跳出循环。

int num = 0;
            for (int a = 1; a <= 100; a++)
            {
                num += a;
            }
            Console.WriteLine(num);
            int num = 0;

for(int a = 1; a <= 100; a++)
            {
                if (a % 7 != 0)
                {
                    int a1 = a % 10;
                    int a2 = a / 10 % 100;
                    int a3 = a / 100;
                    if (a1 != 7 && a2 != 7 && a3 != 7)
                    {
                        Console.WriteLine(a+" ");
                    }
                }
            }

static void Main(string[] args)
        {
            for(int a = 1; a < 10; a++)
            {
                for(int b = 1; b <= a; b++)
                {
                    Console.Write("{0}x{1}={2} ",a,b,a*b);
                }
                Console.WriteLine();
            }
        }