title=Fundamentals of Programming: Built-in data types

From Wikibooks, open books for an open world
Jump to: navigation, search

PAPER 1 - ⇑ Fundamentals of programming ⇑

← Variables Data types Comments →

Most programming languages have built in data types that are used when declaring variables. Some common data types, and the ones you need to know for the exam, are as follows:

Type Description Memory Space Example
Integer a whole number from -2,147,483,648 through 2,147,483,647 4 bytes 37,453
Byte a whole positive number from 0 to 255 1 byte 12
Real Visual Basic does not use Real Numbers, instead it uses {Single} and {Double}, which both allow for decimal places - -
{Single} 1.5 x 10−45 to 3.4 x 1038 4 bytes 1002.375
{Double} 5.0 x 10−324 to 1.7 x 10308 8 bytes 9997.775
Decimal 7.9228 x 10−28 to 7.9228 x 1028 16 bytes 3.8
Boolean either TRUE or FALSE
Alternatively 1 or 0
Alternatively Yes or No
4 bytes (!) TRUE
Character A single character 2 bytes j
String A collection of characters A unicode string with a maximum length of 2,147,483,647 characters cabbage
Date/Time There are several different types of date format that you can apply. 01/01/0001 to 12/31/9999 and times from 12:00:00 AM (midnight) through 11:59:59.9999999 PM 8 bytes 08/17/1924 14:34:23

Using these data types we can start to write a simple computer program:

dim name as string
dim age as integer
name = "Barry"
age = 56.3

Console.writeline("hello " & name & "! you are "  & age & " years old")

But wait a second, this gives you an odd output, it says:

  Blank.svg Code Output
Down arrow Hexagonal Icon.svg

hello Barry! you are 56 years old

I told it that Barry was 56.3 years old! The reason is because I have used an integer to store the age and not a real (single or double) datatype, it therefore drops the decimal part. Integers, afterall, don't store decimal places!


Depending on the datatype, we assign values in different ways:

  • Integers, Bytes, Real, Singles, Doubles = Plain assignment without speech marks
exampleNumber = 7.65
  • Boolean = Plain assignment without speech marks
paidMember = TRUE
  • String, Char = Assignment with speech marks
name = "Henry"
  • Date = Assignment with speech marks
doB= "12/12/45"
Exercise:Data types
Using the correct datatype declare variables for a person's:
  • Age
  • Name
  • Gender
  • Height(metres)
  • Date of Birth
  • license (Do they have a driver license)


dim age as integer
dim name as string
dim gender as char  'OR  dim gender as string
dim height as decimal
dim DoB as date
dim license as boolean
Write assignment statements for the following variables using yourself as an example:
  • Name
  • Age
  • Gender


name = "Peter" 'we must use speech marks for text, so we don't mistake the value for a variable
age = 56 'we don't need speech marks for numbers
gender = "m"
Which of the following declarations correct, which are wrong and why?
dim colour as string
dim wheelNum as integer
dim topSpeed as single
dim hasElectricWindows as char


dim colour as string 'CORRECT, also we could use a single to store the frequency
dim wheelNum as integer 'CORRECT
dim topSpeed as single 'WRONG, we don't need such precision, an integer would do
dim hasElectricWindows as char 'WRONG, a boolean would work better
Which of the following assignments are correct, which are wrong and why:
name = Pete
age = "34"
height = twenty
electricWindow = True


name = Pete 'WRONG, we're assigning a string so we need to use speech marks
name = "Pete"
age = "34" 'WRONG, we're assigning an integer so we don't need speech marks
age = 34
height = "twenty" 'WRONG, height is numeric, so we need to assign a number without speech marks
height = 20
hasElectricWindow = True 'CORRECT assuming you made the change from the previous question
Give two reasons why is it important to get the correct datatypes:


  • Prevents mistakes in code and calculations at run time
  • Makes for smaller and faster programs

Write code that asks the user to insert three numbers with decimals, then outputs them (1) all multiplied together, and (2) added together. For example:

  Blank.svg Code Output
Down arrow Hexagonal Icon.svg

Please insert number 1: 2
Please insert number 2: 3
Please insert number 3: 7.8
multiplied together = 46.8
added together = 12.8


dim num1, num2, num3 as single 'NOT integer, we need decimal numbers!  You can use different identifiers
console.write("Please insert number 1:")
num1 = console.readline()
console.write("Please insert number 2:")
num2 = console.readline()
console.write("Please insert number 3:")
num3 = console.readline()
console.writeline("multiplied together = " & num1 * num2 * num3)
console.writeline("added together = " & num1 * num2 * num3)
Extension: Strongly and weakly typed languages

You don't need to know this part for the exam, but it should help you understand why we need to convert. We have two types of programming language strongly typed and weakly typed. Strongly means that you can't add a string to a integer, even if the string contains a number. Weakly typed allows you to add a string to an integer if the string contains a number

Weak Typing Strong Typing
a = 2
b = '2'

concatenate(a, b) # Returns '22'
add(a, b)         # Returns 4
a = 2
b = '2'

concatenate(str(a), b) # Returns '22'
add(a, int(b))         # Returns 4
concatenate(a, b)     # Type Error
add(a, b)             # Type Error
Languages Visual Basic, Perl, PHP, Rexx Java, C, C++, Python