Joseph Albahari - C# 10 Pocket Reference: Instant Help for C# 10 Programmers

Following is a program that multiplies 12 by 30 and prints the result, 360, to the screen. The double forward slash indicates that the remainder of a line is a comment:

int x = 12 * 30; // Statement 1System.Console.WriteLine (x); // Statement 2

Our program consists of two statements. Statements in C# execute sequentially and are terminated by a semicolon. The first statement computes the expression12 * 30 and stores the result in a variable, named x, whose type is a 32-bit integer (int). The second statement calls the WriteLinemethod on a class called Console, which is defined in a namespace called System. This prints the variable x to a text window on the screen.

A method performs a function; a class groups function members and data members to form an object-oriented building block. The Console class groups members that handle command-line input/output (I/O) functionality, such as the WriteLine method. A class is a kind of type, which we examine in Type Basics.

At the outermost level, types are organized into namespaces. Many commonly used typesincluding the Console classreside in the System namespace. The .NET libraries are organized into nested namespaces. For example, the System.Text namespace contains types for handling text, and System.IO contains types for input/output.

Qualifying the Console class with the System namespace on every use adds clutter. The using directive lets you avoid this clutter by importing a namespace:

using System; // Import the System namespaceint x = 12 * 30;Console.WriteLine (x); // No need to specify System

A basic form of code reuse is to write higher-level functions that call lower-level functions. We can refactor our program with a reusable method called FeetToInches that multiplies an integer by 12, as follows:

using System;Console.WriteLine (FeetToInches (30)); // 360Console.WriteLine (FeetToInches (100)); // 1200int FeetToInches (int feet){int inches = feet * 12;return inches;}

Our method contains a series of statements surrounded by a pair of braces. This is called a statement block.

A method can receive input data from the caller by specifying parameters and output data back to the caller by specifying a return type. Our FeetToInches method has a parameter for inputting feet, and a return type for outputting inches:

int FeetToInches (int feet)...

The literals30 and 100 are the arguments passed to the FeetToInches method.

If a method doesnt receive input, use empty parentheses. If it doesnt return anything, use the void keyword:

using System;SayHello();void SayHello(){ Console.WriteLine ("Hello, world");}

Methods are one of several kinds of functions in C#. Another kind of function we used in our example program was the *operator, which performs multiplication. There are also constructors, properties, events, indexers, and finalizers.