Introduction to Programming with C#

Variable Types & Initialising Variables

Introduction to Variables

A variable is a storage location that holds a value. You can think of a variable as a box in the computer’s memory holding temporary information. You must give each variable in a program an unambiguous name that uniquely identifies it in the context in which it is used. You use a variable’s name to refer to the value it holds. For example, if you want to store the value of the cost of an item in a store, you might create a variable simply called cost and store the item’s cost in this variable. Later on, if you refer to the cost variable, the value retrieved will be the item’s cost that you stored there earlier.

Working with Primitive Data Types

C# has a number of built-in types called primitive data types. The following table lists the most commonly used primitive data types in C# and the range of values that you can store in each.

|Type |Description |Size (in bits) |Range |
|int |Whole numbers |32 |-2147483648 to 2147483647 |
|long |Whole numbers (larger range than int |64 |-9223372036854775808 to 9223372036854775807 |
| |data type) | | |
|float |Floating point numbers |32 |7 digits |
|double |Double precision |64 |15-16 digits |
| |(more accurate than float type) | | |
|decimal |Monetary values |128 |28-29 decimal places |
|string |Sequence of characters |16 bits per character |Not applicable |
|char | |16 |0 to 65535 |
|bool |Boolean |8 |True or False |

Naming Variables

You should adopt a naming convention for variables that helps you avoid confusion concerning the variables you have defined. The following list contains some general recommendations:

• Don’t start an identifier with an underscore. • Don’t create identifiers that differ only by case. For example, do not create one variable named myVariable and another named MyVariable for use at the same time because it is too easy to get them confused. • Start the name with a lowercase letter. • In a multiword identifier, start the second and each subsequent word with an uppercase letter. (This is called camelCase notation.)

Important You should treat the first two of these recommendations as compulsory because they relate to Common Language Specification (CLS) compliance. If you want to write programs that can interoperate with other languages, such as Microsoft Visual Basic, you must comply with these recommendations.

For example, score, footballTeam, _score, and FootballTeam are all valid variable names, but only the first two are recommended.

Declaring Variables

Variables hold values. C# has many different types of values that it can store and process — integers, floating-point numbers, and strings of characters, to name three. When you declare a variable, you must specify the type of data it will hold.

You declare the type and name of a variable in a declaration statement. For example, the following statement declares that the variable named age holds int (integer) values. As always, the statement must be terminated with a semicolon.

int age;

The variable type int is the name of one of the primitive C# types, integer, which is a whole number.

After you’ve declared your variable, you can assign it a value. The following statement assigns age the value 42. Again, you’ll see that the semicolon is required.

age = 42;

The equal sign (=) is the assignment operator, which assigns the value on its right to the variable on its left. After this assignment, the age variable can be used in your code to refer to the value it holds. The next statement writes the value of the age variable, 42, to the console:
Console.WriteLine(age);

Task

Open C# and enter the following code and run it.

|Program Code |
| |
|using System; |
|using System.Collections.Generic; |
|using System.Linq; |
|using System.Text; |
| |
|namespace ConsoleApplication1 |
|{ |
|class Program |
|{ |
|static void Main(string[] args) |
|{ |
| |
|[pic] |
|} |
| |
| |
|} |
|} |

Remember to save your finished program.
Task

1. Create a program that asks the user to enter their name, first line of their address, town, county, post code and prints out the following message

Welcome {username}, you live at: first line of their address town county post code

2. Create a program that asks the user to enter their title (Mr, Mrs etc), firstname, their initial, their lastname, favourite colour, favourite band and prints out the information into a message of your choice.