C# 语法练习(8): 函数

无参、无返回值的函数:

---

using System;

class MyClass
{
    static void Show()
    {
        Console.WriteLine("function");
    }

    static void Main()
    {
        Show();  //function
        Console.ReadKey();
    }
}

参数:

---

using System;

class MyClass
{
    static void Show(string str)
    {
        Console.WriteLine("is " + str);
    }

    static void Main()
    {
        show("function");  //is function
        Console.ReadKey();
    }
}

返回值:

---

using System;

class MyClass
{
    static string Show(string str)
    {
        return "is " + str;
    }

    static void Main()
    {
        string s = Show("function");
        Console.WriteLine(s);  //is function
        Console.ReadKey();
    }
}

函数见 return 就返回:

---

using System;

class MyClass
{
    static int Math(int x, int y)
    {
        return x + y;
        return x * y; /* 执行不了这句 */
    }

    static void Main()
    {
        Console.WriteLine(Math(3,4)); //7
        Console.ReadKey();
    }
}

数组参数:

---

using System;

class MyClass
{
    static int ArrMax(int[] arr)
    {
        int max = arr[0];
        for (int i = 1; i < arr.Length; i++)
            if (arr[i] > max) max = arr[i];
        return max;
    }

    static void Main()
    {
        int[] ns = { 1,2,3,4,5,4,3,2,1 };
        Console.WriteLine(ArrMax(ns));    //5
        Console.ReadKey();
    }
}

参数数组(关键字 params):

---

using System;

class MyClass
{
    static int Sum(params int[] arr)
    {
        int count = 0;
        foreach(int i in arr) count += i;
        return count;
    }

    static void Main()
    {
        int n = Sum(1,2,3);
        Console.WriteLine(n);        //6

        n = Sum(1,2,3,4,5,6,7,8,9);
        Console.WriteLine(n);        //45

        Console.ReadKey();
    }
}

引用参数和输出参数:

---

using System;

class MyClass
{
    static void proc1(ref int num)
    {
        num = num * num;
    }

    static void proc2(out int num)
    {
        num = 100;
    }

    static void Main()
    {
        int a = 9;
        proc1(ref a);  /* 引用参数(ref) 参数必须是已初始化的 */
        Console.WriteLine(a); //81

        int b;
        proc2(out b);  /* 输出参数类似 ref(但初始化不是必要的), 是从函数中接出一个值来 */
        Console.WriteLine(b); //100

        Console.ReadKey();
    }
}

重载:

---

using System;

class MyClass
{
    static int Add(int n1, int n2)
    {
        return n1 + n2;
    }

    static string Add(string s1, string s2)
    {
        return s1 + s2;
    }

    static void Main()
    {
        Console.WriteLine(Add(111,222));      //333
        Console.WriteLine(Add("111", "222")); //111222

        Console.ReadKey();
    }
}

委托(我觉得委托就是把函数当作一种类型的手段):

---

using System;

class MyClass
{
    delegate double MyFunType(double n1, double n2);

    static double Add(double n1, double n2) { return n1 + n2; }
    static double Dec(double n1, double n2) { return n1 - n2; }
    static double Mul(double n1, double n2) { return n1 * n2; }
    static double Div(double n1, double n2) { return n1 / n2; }

    static void Main()
    {
        MyFunType Fun;

        Fun = new MyFunType(Add); Console.WriteLine(Fun(3, 2)); // 5
        Fun = new MyFunType(Dec); Console.WriteLine(Fun(3, 2)); // 1
        Fun = new MyFunType(Mul); Console.WriteLine(Fun(3, 2)); // 6
        Fun = new MyFunType(Div); Console.WriteLine(Fun(3, 2)); // 1.5

        Console.ReadKey();
    }
}

调用外部函数:

---

using System;
using System.Runtime.InteropServices;

class MyClass
{
    [DllImport("User32.dll")]
    public static extern int MessageBox(int h, string m, string c, int type);

    static void Main()
    {
        string str = "Visual Studio 2008!";
        MessageBox(0, str, "信息提示", 0);
    }
}