16讲-语句

声明语句：

  //type/var identifier   (=   local-variable-initializer 初始化器：是一个表达式)
  var x=100;
  int[] y={1,2,3);
  string name="美容";

迭代(循环)语句：

• while 语句按不同条件执行一个嵌入语句（循环体）零次或多次
• do while 语句按不同条件执行一个嵌入语句一次或多次
• for 计数循环
• foreach语句用于枚举一个集合的元素，并对该集合中的每个元素执行一次相关的嵌入语句

do while

    static void Main(string[] args)
        {
            int score = 0;
            bool canContinue= true;
            do
            {
                Console.WriteLine("input first number:");
                string str1 = Console.ReadLine();
                if (str1.ToLower()=="end")
                {
                    break;
                }

                int num1 = 0;
                try
                {
                   num1 = int.Parse(str1);
                }
                catch (OverflowException e)
                {
                    Console.WriteLine(e.Message);
                    continue;
                }
                catch (Exception)
                {
                    throw; continue;
                }

                Console.WriteLine("input second number:");
                string str2 = Console.ReadLine();
                if (str2.ToLower() == "end")
                {
                    break;
                }

                int num2 = 0;

                try
                {
                    num2 = int.Parse(str2);
                }
                catch (OverflowException e)
                {
                    Console.WriteLine(e.Message);
                    continue;
                }
                catch (Exception)
                {
                    throw; continue;
                }

                int sum = num1 + num2;
                if (sum == 100)
                {
                    score++;
                    Console.WriteLine("{0}+{1}={2}", num1, num2, sum);
                }
                else
                {
                    Console.WriteLine("{0}+{1}={2}", num1, num2, sum);
                    canContinue = false;
                }
            } while (canContinue);
            Console.WriteLine("the total score is : {0}",score);

        }

for

   static void Main(string[] args)
   {
         for (int i = 0; i < 9; i++)
            {
                for (int j = 0; j <= i; j++)
                {
                    Console.Write("{0}*{1}={2}  ", i + 1, j + 1, (i + 1) * (j + 1));
                }
                Console.WriteLine();
            }
   }

foreach

• 什么样的集合可以被遍历
• 迭代器

下述为集合遍历的底层原理和迭代器，foreach语句就是对集合遍历的简记法。
            int[] arrList = { 1, 2, 3, 4, 5, 6 };

            Console.WriteLine(arrList.GetType().FullName);// gettype 返回值为type类型，并且，type具有fullname属性
            Console.WriteLine(arrList is Array);//array 继承了Ienumerable接口，故有获得迭代器方法GetEnumerator()

            IEnumerator enumerator = arrList.GetEnumerator();
            while (enumerator.MoveNext())
            {
                Console.WriteLine(enumerator.Current);
            }
            enumerator.Reset();
            enumerator.MoveNext();
            Console.WriteLine(enumerator.Current);//迭代器三个常用成员:movenext()、reset()、current属性

// foreach简单方法
          foreach (var current in arrList)
            {
                Console.WriteLine(current);
            }

//另一个例子
            List<int> intList = new List<int>() { 1,2,3,4}; //泛型，等效于ArrayList

            IEnumerator enumerator1 = intList.GetEnumerator();
            while (enumerator1.MoveNext())
            {
                Console.WriteLine(enumerator1.Current);
            }