C#经典案例实现（求单词在句子出现的次数，字符串倒序输出，用泛型实现两数交换等）

求单词在句子出现的次数

class Cishu
    {
        public static void Getnum()
        {
            string str="The quick brown fox jumped over the lazy dog keeps the doctor away.Can a fox and a dog be friends?";
            string key="the";
            int count=0;
            for(int i = 0; i < str.Length - key.Length; i++)
            {
                if (str.Substring(i, key.Length) == key)
                {
                    count++;
                }
            }
            Console.WriteLine(key +"在" +str+"中出现" + count+"次");

        }
    }

字符串倒序输出

class Daoxu
    {
        public static void Input()
        {
            string str = "this is string";
            char[] ch= str.ToArray();
            Array.Reverse(ch);
            str = new string(ch);
            Console.WriteLine(str);
        }
    }

用泛型实现两数交换

class Program
    {
        static void Swap<T>(ref T x,ref T y)
            {
                T Z = x;
                 x = y;
                 y = Z;

            }
        public static void Main(string[] args)
        {


            

            string x = "hello";
            string y = "world";
            Console.WriteLine("{0},{1}", x, y);
            Swap<string>(ref x, ref y);
            Console.WriteLine("{0},{1}", x, y);
            Console.ReadKey();


           

           




        }
       

    }

求雇员们的总工资

class Employee
    {
      public string empName { get; set; }
       public float empWage { get; set; }
        public static void Main(string[] args)
        {
            List<Employee> list = new List<Employee>();
            list.Add(new Employee() { empName = "李一", empWage = 20 });
            list.Add(new Employee() { empName = "张三", empWage = 30 });
            list.Add(new Employee() { empName ="王二",  empWage= 50 });
            list.Add(new Employee() { empName ="赵四",   empWage=90});
            float sum=0;
            list.ForEach(x => { sum += x.empWage; });
            Console.WriteLine(sum);

        }


    }

还原

class Huanyuan
    {
        public static void Huan()
        { 
            for(int i = 100; i <=999; i++)
            {
                int j = i * 100 + 95;
                if(j%57==0 && j % 67 == 0)
                {
                    Console.WriteLine(j);
                }
            }
        }
    }

求圆的周长，面积，体积

 class MyMath
    {
       
        public static void Perimeter(double R)
        {
            double c = 2 * Math.PI * R;
            Console.WriteLine(c);
        }
        public static void Area(double R)
        {
            double s = Math.PI * R * R;
            Console.WriteLine(s);
        }
        public static void Voiume(double R)
        {
            double v= (3/4)*Math.PI*R*R*R;
            Console.WriteLine(v);
        }

百钱百鸡

class Maiji
    {
        public static void Buy()
        {
            for(int i = 0; i < 20; i++)
            {
                for (int j = 0; j < 33; j++)
                {
                    if ((100 - i - j)%3==0 && i * 5+ j * 3+ (100 - i - j) / 3 == 100)
                    {
                        Console.WriteLine("{0},{1},{2}", i, j, 100 - i - j);
                    }
                }
            }
        }
    }

输出年份

class Nianfen
    {
        public static void Put()
        {
            float i = 1.334f;
            int n = 123;
            string s1 = string.Format("{0:F3}", i);
            Console.WriteLine(s1);
            string s2 = string.Format("{0:p}", i);
            Console.WriteLine(s2);
            string s3 = string.Format("{0:00000}", n);
            Console.WriteLine(s3);
            DateTime dt = new DateTime(2020, 9, 24);
            string str = dt.ToString("yyyy年MM月d日");
            Console.WriteLine(str);
        }
    
    }

求100以内的质数

class Zishu
    {
        public static void Shu()
        {
            for(int i = 2; i <= 100; i++)
            {
                int j = 2;
                while (i % j != 0)
                {
                    j++;
                }
                if (i == j)
                {
                    Console.WriteLine(i);
                }
            }
        }
    }