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函数

public void First()
        {
            Console.WriteLine("这是我第一个函数的第一句话。");

        }
static void Main(string[] args)
        {

            Program hanshu = new Program();    //实例化   初始化  这个类
            //hanshu.First();
         }

//格式一：没有参数，没有返回值（无参无返）
        /// <summary>
        /// 累加求和，没有参数没有返回值
        /// </summary>
        public void LeiJia()
        {
            Console.Write("请输入一个正整数：");
            int a = int.Parse(Console.ReadLine());
            int sum=0;
            for (int i = 1; i <= a;i++ )
            {
                sum += i;
            }
            Console.WriteLine("sum="+sum);
        }
 static void Main(string[] args)
        {
            Program hanshu = new Program(); 
            hanshu.LeiJia();//格式1调用
        }

格式一：无参无返

 1         //格式二：有参数，没有返回值（有参无返）
 2         /// <summary>
 3         /// 
 4         /// </summary>
 5         /// <param name="a"></param>
 6         public void LeiJia(int a)
 7         {
 8             int sum = 0;
 9             for (int i = 1; i <= a; i++)
10             {
11                 sum += i;
12             }
13             Console.WriteLine("sum=" + sum);
14         }
15         static void Main(string[] args)
16         {
17             Program hanshu = new Program(); 
18             Console.Write("请输入一个正整数：");
19             int a = int.Parse(Console.ReadLine());
20             hanshu.LeiJia(a);//格式2调用
21         }

格式二：有参无返

 1 /格式三：有参数，有返回值（有参有返）
 2         /// <summary>
 3         /// 
 4         /// </summary>
 5         /// <param name="d"></param>
 6         /// <returns></returns>
 7         public int LeiJia1(int d)
 8         {
 9             int sum = 0;
10             for (int i = 1; i <= d; i++)
11             {
12                 sum += i;
13             }
14             return sum;
15         }
16  static void Main(string[] args)
17         {
18             Program hanshu = new Program();  
19             Console.Write("请输入一个正整数：");
20             int a = int.Parse(Console.ReadLine());
21             int sum=hanshu.LeiJia1(a);
22             Console.WriteLine("sum=" + sum);  //格式3调用
23         }

格式三：有参有返

 1 //格式四：没有参数，有返回值（无参有返）
 2         /// <summary>
 3         /// 
 4         /// </summary>
 5         /// <returns></returns>
 6         public int LeiJia2()
 7         {
 8             Console.Write("请输入一个正整数：");
 9             int a = int.Parse(Console.ReadLine());
10             int sum = 0;
11             for (int i = 1; i <= a; i++)
12             {
13                 sum += i;
14             }
15             return sum;
16         }
17         static void Main(string[] args)
18         {
19             Program hanshu = new Program(); 
20             int sum = hanshu.LeiJia2();
21             Console.WriteLine("sum=" + sum); //格式4调用
22         }

格式四：无参有返

 1 //比较大小
 2         /// <summary>
 3         /// 输出最大的值
 4         /// </summary>
 5         /// <param name="a"></param>
 6         /// <param name="b"></param>
 7         /// <returns></returns>
 8         public double Max(double a,double b)
 9         {
10             if (a > b)
11             {
12                 return a;
13             }
14             else
15             {
16                 return b;
17             }
18         }
19         static void Main(string[] args)
20         {
21             Program hanshu = new Program();
22             double a = 10;
23             double b = 9;
24             double c = 15;
25             double d = hanshu.Max(hanshu.Max(a, b),c);
26             Console.WriteLine(d);
27           }

练习，比较大小，输出最大的值

//求一元二次方程的根

  1 class Class1
  2     {
  3         //格式一：无参无返
  4         public void Jie()
  5         {
  6             Console.Write("a=");
  7             double a = double.Parse(Console.ReadLine());
  8             Console.Write("b=");
  9             double b = double.Parse(Console.ReadLine());
 10             Console.Write("c=");
 11             double c = double.Parse(Console.ReadLine());
 12             if (a == 0)
 13             {
 14                 Console.WriteLine("此方程不是一元二次方程！");
 15             }
 16             else
 17             {
 18                 double d=b*b-4*a*c;
 19                 double x1;
 20                 double x2;
 21                 if(d>0)
 22                 {
 23                     x1=(-b+Math.Sqrt(d))/(2*a);
 24                     x2=(-b-Math.Sqrt(d))/(2*a);
 25                     Console.WriteLine("方程有两个不等实根！x1={0}，x2={1}",x1,x2);
 26                 }
 27                 else if(d==0)
 28                 {
 29                     x1=-b/(2*a);
 30                     Console.WriteLine("方程有两个相等实根！x1=x2={0}", x1);
 31                 }
 32                 else
 33                 {
 34                     Console.WriteLine("方程无实根");
 35                 }
 36             }
 37         }
 38 
 39         //格式二：有参无返
 40         public void Jie(double a, double b, double c)
 41         {
 42             if (a == 0)
 43             {
 44                 Console.WriteLine("此方程不是一元二次方程！");
 45             }
 46             else
 47             {
 48                 double d = b * b - 4 * a * c;
 49                 double x1;
 50                 double x2;
 51                 if (d > 0)
 52                 {
 53                     x1 = (-b + Math.Sqrt(d)) / (2 * a);
 54                     x2 = (-b - Math.Sqrt(d)) / (2 * a);
 55                     Console.WriteLine("方程有两个不等实根！x1={0}，x2={1}", x1, x2);
 56                 }
 57                 else if (d == 0)
 58                 {
 59                     x1 = -b / (2 * a);
 60                     Console.WriteLine("方程有两个相等实根！x1=x2={0}", x1);
 61                 }
 62                 else
 63                 {
 64                     Console.WriteLine("方程无实根");
 65                 }
 66             }
 67         }
 68 
 69         //格式三：有参有返
 70         public string Jie1(double a, double b, double c)
 71         {
 72             string m = "";
 73             if (a == 0)
 74             {
 75                 m="此方程不是一元二次方程！";
 76             }
 77             else
 78             {
 79                 double d = b * b - 4 * a * c;
 80                 double x1;
 81                 double x2;
 82                 
 83                 if (d > 0)
 84                 {
 85                     x1 = (-b + Math.Sqrt(d)) / (2 * a);
 86                     x2 = (-b - Math.Sqrt(d)) / (2 * a);
 87                     m = "方程有两个不等实根！x1="+x1+",x2="+x2;
 88                 }
 89                 else if (d == 0)
 90                 {
 91                     x1 = -b / (2 * a);
 92                     m="方程有两个相等实根！x1=x2="+ x1;
 93                 }
 94                 else
 95                 {
 96                     m="方程无实根";
 97                 }
 98             }
 99             return m;
100         }
101 
102         //格式四：无参有返
103         public string Jie2()
104         {
105             Console.Write("a=");
106             double a = double.Parse(Console.ReadLine());
107             Console.Write("b=");
108             double b = double.Parse(Console.ReadLine());
109             Console.Write("c=");
110             double c = double.Parse(Console.ReadLine());
111             string m = "";
112             if (a == 0)
113             {
114                 m = "此方程不是一元二次方程！";
115             }
116             else
117             {
118                 double d = b * b - 4 * a * c;
119                 double x1;
120                 double x2;
121 
122                 if (d > 0)
123                 {
124                     x1 = (-b + Math.Sqrt(d)) / (2 * a);
125                     x2 = (-b - Math.Sqrt(d)) / (2 * a);
126                     m = "方程有两个不等实根！x1=" + x1 + ",x2=" + x2;
127                 }
128                 else if (d == 0)
129                 {
130                     x1 = -b / (2 * a);
131                     m = "方程有两个相等实根！x1=x2=" + x1;
132                 }
133                 else
134                 {
135                     m = "方程无实根";
136                 }
137             }
138             return m;
139         }
140 
141         static void b(string[] args)
142         {
143             Class1 hanshu = new Class1();
144             //格式一：
145             //hanshu.Jie();
146 
147             //格式二：
148             //Console.Write("a=");
149             //double a = double.Parse(Console.ReadLine());
150             //Console.Write("b=");
151             //double b = double.Parse(Console.ReadLine());
152             //Console.Write("c=");
153             //double c = double.Parse(Console.ReadLine());
154             //hanshu.Jie(a,b,c);
155 
156             //格式三：
157             Console.Write("a=");
158             double a = double.Parse(Console.ReadLine());
159             Console.Write("b=");
160             double b = double.Parse(Console.ReadLine());
161             Console.Write("c=");
162             double c = double.Parse(Console.ReadLine());
163             //string A = hanshu.Jie1(a, b, c);
164             //string[] n = A.Split(' ');
165             //foreach (string m in n)
166             //{
167             //    Console.WriteLine(m);
168             //}
169             string m = hanshu.Jie1(a, b, c);
170             Console.WriteLine(m);
171 
172             //格式四：
173             //string m = hanshu.Jie2();
174             //Console.WriteLine(m);
175 
176 
177 
178             Console.ReadLine();
179         }

四种格式

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原文地址：https://www.cnblogs.com/maxin991025-/p/5968836.html