9号的内容：上午主要是练习两个图题型，下午继续，只是在最后的时候讲的是迭代和穷举。关于这些内容我先整理下文字叙述性的内容，然后再把题型在练习一下。。。

循环：反复执行某段代码。

循环四要素：初始条件，循环条件，循环体，状态改变。

for(初始条件;循环条件;状态改变)

{

循环体

}

break ——中断循环，跳出循环

continue——停止本次循环，进入下次循环

for循环拥有两类：

穷举：

把所有可能的情况都走一遍，使用if条件筛选出来满足条件的情况。

迭代：

从初始情况按照规律不断求解中间情况，最终推导出结果。

while 循环

其实是for循环的变形写法

for(int i = 1; i<=5;i++)

{

循环体；

}

上面的for循环可以写成

int i= 1；

for(;i<=5;)

{

循环体；

i++;

}

写成while就是以下样式

int i= 1；

while（表达式（i<=5））

{

循环体；

状态改变（i++）；

}

do

{

循环体；

状态改变（i++）;

}while（表达式（i<=5））

注意：do while是不管满不满足表达式，我都会先执行一遍。

跳转语句：

break：跳出整个循环

continue：跳出本次循环，继续下次循环。

    练习：输入五遍你好

输入一个正整数，求阶乘

 Console.Write(“请输入一个正整数”);
            int a = int.Parse(Console.ReadLine());
            int sum = 1;
            for (int i = 1; i <= a; i++)
            {
                sum *= i;
            }
            Console.WriteLine(sum);
            Console.ReadLine();

  //输入一个正整数，求和
            Console.Write(“a=”);
            int a = int.Parse(Console.ReadLine());
            int sum = 0;
            for (int i = 1; i <= a; i++)
            {
                sum += i;
            }
            Console.WriteLine(sum);
            Console.ReadLine();

 //求1！+2！+3！+4！+…..+n!
            Console.Write(“请输入n=”);
            int n = int.Parse(Console.ReadLine());
            int sum = 0;
            for (int i = 1; i <= n; i++)
            {
                int sum1 = 1;
                for (int j = 1; j <= i; j++)
                {
                    sum1 *= j;
                }
                sum += sum1;
            }
            Console.WriteLine(sum);
            Console.ReadLine();

//找出100以内和7有关的数

            int a = 0;
            for (int i = 1; i <= 100; i++)
            {
                if (i % 7 == 0 || i % 10 == 7 || i / 10 == 7)
                {
                    a++;
                    Console.WriteLine(i);
                }
            }
            Console.WriteLine(“共” + a + “次”);
            Console.ReadLine();

//一个游戏，前20关是每一关自身的分数，
            //21-30关每一关是10分
            //31-40关，每一关是20分
            //41-49关，每一关是30分
            //50关，是100分

这题有两种解题思路，一种是for嵌套if，一种是if嵌套for，经验证两种的结果一样

            Console.Write(“请输入你的关数a=”);
            int a = int.Parse(Console.ReadLine());
            int sum = 0;
            if (a >= 0 && a <= 50)
            {
                for (int i = 1; i <= a; i++)
                {
                    if (i >= 0 && i <= 20)
                    {
                        sum += i;
                    }
                    else if (i >= 21 && i <= 30)
                    {
                        sum += 10;
                    }
                    else if (i >= 31 && i <= 40)
                    {
                        sum += 20;
                    }
                    else if (i >= 41 && i <= 49)
                    {
                        sum += 30;
                    }
                    else
                    {
                        sum += 100;
                    }
                }
                Console.WriteLine(sum);
            }

            else
            {
                Console.WriteLine(“输入有误”);
            }
            Console.ReadLine();

第二种是：

            Console.Write(“输入关数a=”);
            int a = int.Parse(Console.ReadLine());
            int sum = 0;
            if (a >= 0 && a <= 50)
            {
                if (a >= 1 && a <= 20)
                {
                    for (int i = 1; i <= a; i++)
                    {
                        sum += i;
                    }
                }
                else if (a >= 21 && a <= 30)
                {
                    for (int i = 1; i <= 20; i++)
                    {
                        sum += i;
                    }
                    for (int i = 21; i <= a; i++)
                    {
                        sum += 10;
                    }
                }

                else if (a >= 31 && a <= 40)
                {
                    for (int i = 1; i <= 20; i++)
                    {
                        sum += i;
                    }
                    for (int i = 21; i <= 30; i++)
                    {
                        sum += 10;
                    }
                    for (int i = 31; i <= a; i++)
                    {
                        sum += 20;
                    }
                }
                else if (a >= 41 && a <= 49)
                {
                    for (int i = 1; i <= 20; i++)
                    {
                        sum += i;
                    }
                    for (int i = 21; i <= 30; i++)
                    {
                        sum += 10;
                    }
                    for (int i = 31; i <= 40; i++)
                    {
                        sum += 20;
                    }
                    for (int i = 41; i <= a; i++)
                    {
                        sum += 30;
                    }
                }
                else
                {
                    for (int i = 1; i <= 20; i++)
                    {
                        sum += i;
                    }
                    for (int i = 21; i <= 30; i++)
                    {
                        sum += 10;
                    }
                    for (int i = 31; i <= 40; i++)
                    {
                        sum += 20;
                    }
                    for (int i = 41; i <= 49; i++)
                    {
                        sum += 30;
                    }
                    sum += 100;
                }
            }
            else
            {
                Console.WriteLine(“输入有误”);
            }
            Console.WriteLine(sum);
            Console.ReadLine();

 //乘法口诀

            for (int i = 1; i <= 9; i++)
            {
                for (int j = 1; j <= i; j++)
                {
                    Console.Write(“” + j + “*” + i + “=” + (i * j) + ” “);
                }
                Console.WriteLine();
            }
            Console.ReadLine();

            ////单位给发了一张150元购物卡，
            //拿着到超市买三类洗化用品。
            //洗发水15元，香皂2元，牙刷5元。
            //求刚好花完150元，有多少种买法，
            //每种买法都是各买几样？
            //设买的洗发水x,150/15==10
            //设买的牙刷 y，150/5=30
            //设买的香皂  z，150/2=75

            int biao = 0;
            int m = 0;
            for (int x = 0; x <= 10; x++)
            {
                for (int y = 0; y <= 30; y++)
                {
                    for (int z = 0; z <= 75; z++)
                    {
                        m++;
                        if (15 * x + 5 * y + 2 * z == 150)
                        {
                            biao++;
                            Console.WriteLine(“这是第” + biao + “中共有洗发水” + x + “瓶，香皂” + z + “块，牙刷” + y + “只”);
                        }
                    }

                }
            }
            Console.WriteLine(“共有” + biao + “中”);
            Console.WriteLine(m);
            Console.ReadLine();

截取一部分，25916是运行的次数

 //纸张可以无限次对折，纸张厚度为0.07毫米。
            //问多少次对折至少可以超过8848？

            //0.07—-7,884800000
            int a = 7;
            int i = 0;   //int i=1;
            for (; ; )
            {
                a *= 2;
                i++;
                if (a >= 884800000)
                {
                    Console.WriteLine(a);
                    Console.WriteLine(i);
                    break;
                }
                         //i++;
            }
            Console.ReadLine();

几何倍增的威力是很大的

以上就是内容的复习