20190322-C#學習日誌

using System; //使用System的命名空間

/*--------------------------------------------------------------------------------------------------*/

namespace First
{
    class MyClass
    {
    }
}
namespace Second
{
    class MyClass
    {
    }
}

/*--------------------------------------------------------------------------------------------------*/

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

/*--------------------------------------------------------------------------------------------------*/

//變數(Variable),儲存數據的名稱

int userAge; //宣告整數

byte userAge; //宣告位元組

float pi = 3.142f; //宣告32位元浮點值

double pi = 3.142; //宣告64位元的浮點值

decimal pi = 3.142m; //宣告較高精準度的浮點

char c = 'A'; 宣告字元

bool b = true; //宣告布林值 true 或者 false

/*--------------------------------------------------------------------------------------------------*/

//Camel Casing
string thisIsAVariableName; // 駝峰式大小寫

//underscores to separate words
string this_is_a_variable_name; //將不同單字用下底線隔開

/*--------------------------------------------------------------------------------------------------*/

//初始化變數

byte = userAge = 20;

int numberOfEmployees = 510;

double numberOfHours = 5120;

float hourlyRate = 60.0f;

decimal income = 25399.65m;

char grade = '#';

bool isLoggedIn = true;

byte level = 2, userExperience = 5;

byte year;

year = 20;

/*--------------------------------------------------------------------------------------------------*/

int x = 5; //一個等於是將等號右邊的值複製給等號左邊

int y = 10;

x = y; //將 y 的值複製到 x

Console.WriteLine(x); //顯示 10

/*--------------------------------------------------------------------------------------------------*/

//基本的運算符號

int x = 7, y = 2;

Console.WriteLine( x + y ); // 9

Console.WriteLine( x - y ); // 5

Console.WriteLine( x * y ); // 14

Console.WriteLine( x / y ); // 3

Console.WriteLine( x % y ); // 1

double x = 7;

int y = 2;

Console.WriteLine( x / y ); // 3.5

/*--------------------------------------------------------------------------------------------------*/

int x = 10;

x = x + 2; // 12

x += 2;

x -= 2;

x++; //先賦值在運算

++x; //先運算在賦值

/*--------------------------------------------------------------------------------------------------*/

//類型的轉換

int x = (int)20.9;

float num1 = (float)20.9;

decimal num2 = (decimal)20.9;

/*--------------------------------------------------------------------------------------------------*/

//數組(Arrary)

int [] userAge = {21, 22, 23, 24, 25};

int [] userAge2;

userAge2 = new[] {21, 22, 23, 24, 25};

int [] userAge3 = new int[5]; // {0, 0, 0, 0, 0}

//index
userAge3[0] = 31; // {31, 0, 0, 0, 0}

userAge3[2] = userAge3[2] + 20; // {31, 0, 20, 0, 0}

/*--------------------------------------------------------------------------------------------------*/

int [] userAge = {22, 21, 23, 18, 25};

Console.WriteLine(userAge.Length); //取得數組內有多少筆資料

Array.Sort(userAge); //自動排序數組 {18, 21, 22, 23, 25}

//IndexOf
int [] numbers = {10, 30, 44, 21, 51, 21, 61, 24, 14};
int ans = Array.IndexOf(numbers, 21);
// 3, 尋找是否有此筆資料, 並返回Index, 如果找不到為-1

/*--------------------------------------------------------------------------------------------------*/

//字串

string message = "Hello World";

string message2 = "Hello World, " + " my name is Kent";

int ans = message.Length; //取得字串裡面有多少字元

Console.WriteLine(message.Substring(2)); // "llo World"

Console.WriteLine(message.Substring(2, 5)); // "llo W"
// Substring(2, 5) 起始位置, 字元的長度

/*--------------------------------------------------------------------------------------------------*/

string FirstString = "This is John";

string SecondString = "Hello";

// Equals 比較字符串是否相同

FirstString.Equals("This is John"); // true

FirstString.Equals(SecondString); // false

/*--------------------------------------------------------------------------------------------------*/

//將字串分開

char [] separator = { ' , ' , ' ; ' };

string fruits = "Apple, Banana; Dureian, , Mango";

string [] substrings = fruits.Split(separator);

Console, WriteLine(substrings);

/*--------------------------------------------------------------------------------------------------*/

//列表(Lists)

List<int> userAgeList = new List<int>();

List<int> userAgeList = new List<int>{11, 21, 31, 41};

//Add, 將資料加入List的最後

userAgeList.Add(51);

userAgeList.Add(61);

//Insert, 將資料加入指定的Index

userAgeList.Insert(2, 51);

//Remove, 將第一次找到的指定資料移除

userAgeList.Remove(51);

//RemoveAt, 將指定的Index移除

userAgeList.Remove(2);

//Contains, 檢查資料是否在List裡，並回傳布林值

userAgeList.Contains(51);

//Clear, 將List裡的資料全部清除

userAgeList.Clear();

/*--------------------------------------------------------------------------------------------------*/

// value type
int myNumber = 5;

//reference
string message = "Hello";