C# Tutorial - 4. Statements and Expression Tutorial

本文主要介紹C#最基本要件和運算式，以供有興趣的朋友參考。

Statements

Statement為C#最基本的組成，所有程式都是由Statement建構的，可以宣告區域變數、常數、呼叫方法、建立物件，或指派值給變數、屬性或欄位。

Statement通常以分號結尾。

常見的Statements

分類	C# 關鍵字
Declaration statements	xx=2
Expression statements	area = 3.14 * (radius * radius);
Selection statements	if、else、switch、case
Iteration statements	do、for、foreach、in、while
Jump statements	break、continue、default、goto、return、yield
Exception handling statements	throw、try-catch、try-finally、try-catch-finally

Msdn Example:

    static void Main()

    {

        // Declaration statement.

        int counter;

        // Assignment statement.

        counter = 1;

        // Error! This is an expression, not an expression statement.

        // counter + 1; 

        // Declaration statements with initializers are functionally

        // equivalent to pointA declaration statement followed by assignment statement:         

        int[] radii = { 15, 32, 108, 74, 9 }; // Declare and initialize an array.

        const double pi = 3.14159; // Declare and initialize pointA constant.          

        // foreach statement block that contains multiple statements.

        foreach (int radius in radii)

        {

            // Declaration statement with initializer.

            double circumference = pi * (2 * radius);

            // Expression statement (method invocation). A single-line

            // statement can span multiple text lines because line breaks

            // are treated as white space, which is ignored by the compiler.

            System.Console.WriteLine("Radius of circle #{0} is {1}. Circumference = {2:N2}",

                                    counter, radius, circumference);

            // Expression statement (postfix increment).

            counter++;

        } // End of foreach statement block

    } // End of Main method body.

} // End of SimpleStatements class.

Expression

運算式是程式碼片段，可判定為單一的值、物件、方法或命名空間。

運算式可包含常值、方法引動過程、運算子和運算元，或「簡單名稱」(Simple Name)。簡單名稱可以是變數的名稱、型別成員、方法參數、命名空間或型別。

Msdn example:

((x < 10) && ( x > 5)) || ((x > 20) && (x < 25))

System.Convert.ToInt32("35")