Visual C# Guide
Variables & Data Types
Selection
Iteration/Repetition
Procedures & Functions
Built-in Functions
Arrays
Handling Text Files
Standard Algorithms
Validation & Error Handling
Using Classes
Floppy Cube Project
Odds & Sods
Visual C# Guide
Data Types
When we want to use a variable in a C# program, we must first declare the variable.
When programming, it is often necessary to store information so that it can be used at a later time in a program. In low level languages, the programmer specifies the exact location (in memory or in a particular register of the processor) where the information is stored. In high level languages, we use variables to represent stored information.
Imagine a series of boxes, each one with a label on the front to name the box. These names are called variables in C#. The contents of each box is the information stored in the variable.
It is useful to give variables meaningful names that can be easily understood by the programmer (you).
There are rules about variable names in C#.
Variable Names
The name that you give to a variable should help you to remember what the variable was to be used for. In C#, it is usual to use camelCase when writing variable names. A variable name must be a single word with no spaces. It should start with a lower case letter. If two or more words are combined together into a single variable name, we captialize the first letter of each word after the first. For example,
numberOfEntries = 5;
wholeNumber1 = 7;
Keywords
The following words are used in the C# language and cannot be used as variable names.
| abstract | as | base | bool |
| break | byte | case | catch |
| char | checked | class | const |
| continue | decimal | default | delegate |
| do | double | else | enum |
| event | explicit | extern | false |
| finally | fixed | float | for |
| foreach | get | goto | if |
| implicit | in | int | interface |
| internal | is | lock | long |
| namespace | new | null | object |
| operator | out | override | params |
| partial | private | protected | public |
| readonly | ref | return | sbyte |
| sealed | set | short | sizeof |
| stackalloc | static | string | struct |
| switch | this | throw | true |
| try | typeof | uint | ulong |
| unchecked | unsafe | ushort | using |
| value | virtual | void | volatile |
| where | while | yield |
Built-In Data Types
The following lines are examples of variable declarations in C#. The word, int specifies that the integer data type will be used. You have a choice about whether to initialize the variable in its declaration statement.
int myWholeNumber;
int anotherWholeNumber = 5;
| Data Type | Description | Memory Allocated | Range |
| int | Signed 32-bit integer | 4 bytes | -2147483648 to 2147483647 |
| byte | Unsigned 8-bit integer | 1 byte | 0 to 255 |
| long | Signed 64-bit integer | 8 bytes | -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 |
| double | Double-precision floating-point number | 8 bytes | Precise to about 15-16 digits |
| decimal | Suitable for monetary calculations | 16 bytes | Precise to 28-29 significant digits |
| char | Stores a single Unicode character. | 2 bytes | |
| string | Strings are enclosed in double quotes. | As required | |
| bool | Boolean value (either true or false) |
Declaring Constants
A constant is a programmer-specified value that does not change throughout the lifetime of the program. Think of it as a variable that you cannot change. To declare a constant in C#, you do the following,
const double pi = 3.141593;
Notice that you use the keyword, const followed by the data type.
Local & Global Variables - Scope
The scope of a variable determines which parts of the program can access its values. The variables in the program on the next page are all local variables. That means that they can only be used within the block of code where they are declared.
Global variables are declared for use throughout the program. We will meet more of these later. It is not always desirable to use global variables in complex programs since it can be easy to change the value by accident.