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

Data Types

What are Variables? What are Variables? The Data Types supported by VB Understand why Data Types are used

When a program runs, any data it uses must be stored in RAM When a program runs, any data it uses must be stored 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”)

To declare a variable means to tell Visual Basic two things about it To declare a variable means to tell Visual Basic two 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

You can declare more than one variable of the same type in the same line of code, for example You can declare more than one variable of the same type in the same line of code, for example Dim FirstNumber, SecondNumber, ThirdNumber As Integer

See “Data Types” document See “Data Types” document

Data Types are used to determine what type of information is going to be stored in a variable (will it be a date, a number or some text) Data Types are used to determine what 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

Data Types are also used to help 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) Data Types are also used to help 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

Having different Data Types allows you to perform calculation on the different values of variable (such as Adding values of variables) Having different Data Types allows you to 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

Accurate storage Accurate storage This is vitally important for numeric 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

Calculations Calculations Data that you need to do calculations 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)

Create a table in word to list 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) Create a table in word to list 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