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if语句

1、if(判断)                   2、 if(判断)                     3、 if(判断1)                           4、if(判断1)

    {                                     {                                      {                                             {

      (语句)                                (语句1)                           if(判断2)                                 (语句1)

    }                                     }                                          {                                          }

                                           else                                          (语句1)                          else if(判断2)

                                          {                                            }                                         {

                                                (语句2)                              else                                           (语句2)

                                           }                                           {                                          }

                                                                                             (语句2)                                      ……

                                                                                         }                                         else

                                                                                     else                                                (语句3)

                                                                                        (语句3)

 

例:

1、解方程a*x*x+b*x+c=0

             Console.WriteLine("求方程ax*x+bx+c=0的根的情况");

             Console.Write("a=");

             int a = Convert.ToInt32(Console.ReadLine());

             Console.Write("b=");

             int b = Convert.ToInt32(Console.ReadLine());

             Console.Write("c=");

             int c = Convert.ToInt32(Console.ReadLine());

             if (a == 0)

             {

                 Console.WriteLine("不是一元二次方程");

             }

             else

             {

                 Console.WriteLine("一元二次方程");

                 int derta = b * b - 4 * a * c;

                 if (derta > 0)

                 {

                     double x1 = (-b + Math.Sqrt(derta)) / (2 * a);

                     double x2 = (-b - Math.Sqrt(derta)) / (2 * a);

                     Console.WriteLine("有两个不等的实根:");

                     Console.WriteLine("x1=" + x1);

                     Console.WriteLine("x2=" + x2);

                }

                 else if (derta == 0)

                 {

                     Console.WriteLine("有两个相等的实根:");

                     double m = -b / (2 * a);

                     Console.WriteLine("x=" + m);

                 }

                 else

                     Console.WriteLine("无实根");

             }

 

2、判断体重是否标准

             Console.Write("性别:");

             bool sex=Console.ReadLine()=="男";

             Console.Write("身高(cm):");

             int hight=Convert.ToInt32(Console.ReadLine());

             Console.Write("体重(kg):");

             int weight=Convert.ToInt32(Console.ReadLine());

 

            if (sex == true)

             {

                 int s=hight-100;

                 if (weight > (s + 3))

                 {

                     Console.WriteLine("胖");

                 }

                 else if((weight<=(s+3))&&(weight>=(s-3)))

                 {

                     Console.WriteLine("正常");

                 }

                 else

                     Console.WriteLine("瘦");

             }

             else

             {

                 int s=hight-110;

                 if (weight > (s + 3))

                 {

                     Console.WriteLine("胖");

                 }

                 else if((weight<=(s+3))&&(weight>=(s-3)))

                 {

                     Console.WriteLine("正常");

                 }

                 else

                     Console.WriteLine("瘦");

             }

 

3、跟电脑猜拳

            Console.Write("请出拳:");

            string human = Console.ReadLine();

            Console.WriteLine("人VS电脑:");

 

            Random a = new Random();

            int x = a.Next(3);

            String computer;

            if (x == 0)

            {

                computer="剪刀";

            }

            else if (x == 1)

            {

                computer = "石头";

            }

            else

                computer = "布";

 

            Console.WriteLine(human + "VS" + computer);

            int b = 3;

            if (human != "剪刀" && human != "石头" && human != "布")

            {

                Console.WriteLine("输入错误");

            }

            else if (human == "剪刀")

            {

                 b = 0;

            }

            else if (human == "石头")

            {

                b = 1;

            }

            else

                b = 2;

 

            if (( b - x == 1) || (x - b == 2))

            {

                Console.WriteLine("你赢了");

            }

            else if (( x - b == 1) || (b - x == 2))

            {

                Console.WriteLine("你输了");

            }

            else if (b == x)

            {

                Console.WriteLine("平局");

            }

            else

                Console.WriteLine("错误");