Unit 6: Software Design & Development. Data Types in Programming презентация

are used

in RAM

A variable is a name made up by a programmer to identify the address in RAM where a piece of data is stored

Every variable must be of a given data type (see word document “Data Types”)

things about it
Its name
Its data type

Use the keywords Dim and As when you declare a variable, for example
Dim Number As Integer
Dim Payment As Decimal
Dim DateOfPayment As Date

type in the same line of code, for example

Dim FirstNumber, SecondNumber, ThirdNumber As Integer

type of information is going to be stored in a variable (will it be a date, a number or some text)

Data Types also determine how much space in memory (RAM) the variable needs to store the information

Each Data Type has a maximum size (this is what has the impact on memory)

Important to choose the correct Data Type for variables to ensure that the most efficient amount of storage space needed is used

validate what is being stored in each variable (since VB will present you with an error message if you put a different type of value in a variable with the wrong data type)

For example, VB will not let you put text or numbers into a variable with a Date data type

And VB will not let you put text into a field with a Number data type

The result will be that the program will “fall-over” displaying an error message

perform calculation on the different values of variable (such as Adding values of variables)

Having different Data Types also allows different formatting to be applied to the field when you create reports or data entry screen

For example, a Date field in VB (just like in Access) can be printed or displayed with the following different formats
11/09/2011
11 Sept 2011
11 September 2011

values. If the data type is too small to store a value, it becomes truncated (chopped) and accuracy is lost.
Using a data type of the right size prevents this happening

Efficiency of storage
This is important particularly in computer systems where free RAM or processing power may be limited

Additional validation
Entering non-numeric data into a numeric data type can cause a program to crash at runtime

with must be placed in a numeric data type such as integer or single
Placing non-numeric data into these variables, will result in the program crashing

Formatting
By having data types you can take advantage of the formatting that can be applied to each type and make the presentation of information stored in variable appear more user friendly

Consistency
Data types give the programmer the ability to have variables that have a consistent style throughout the program (with a consistent format and options)

some of the data types that are available in Visual Basic, with their size, space taken up (in RAM) and the short/brief description of the type of data that should be stored in the data type (include some examples)

Under the table provide a description of the benefits gained by having a variety of different data types available when producing programs