C# 文法練習(8): 函數

無參、無傳回值的函數:

using System;class MyClass{    static void Show()    {        Console.WriteLine("function");    }    static void Main()    {        Show();  //function        Console.ReadKey();    }}

參數:

using System;class MyClass{    static void Show(string str)    {        Console.WriteLine("is " + str);    }    static void Main()    {        show("function");  //is function        Console.ReadKey();    }}

傳回值:

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();    }}

函數見 return 就返回:

using System;class MyClass{    static int Math(int x, int y)    {        return x + y;        return x * y; /* 執行不了這句 */    }    static void Main()    {        Console.WriteLine(Math(3,4)); //7        Console.ReadKey();    }}

數組參數:

using System;class MyClass{    static int ArrMax(int[] arr)    {        int max = arr[0];        for (int i = 1; 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();    }}

參數數組(關鍵字 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();    }}

引用參數和輸出參數:

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);  /* 引用參數(ref) 參數必須是已初始化的 */        Console.WriteLine(a); //81        int b;        proc2(out b);  /* 輸出參數類似 ref(但初始化不是必要的), 是從函數中接出一個值來 */        Console.WriteLine(b); //100        Console.ReadKey();    }}

重載:

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();    }}

委託(我覺得委託就是把函數當作一種類型的手段):

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();    }}

調用外部函數:

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, "資訊提示", 0);    }}