Pascal Programming

1
Pascal Programming

• Variables, Constants
• and Data Types
• Carl Smith
• National Certificate Unit 4

2
What is a variable

• A variable is a named reference to a storage area
  in reserved memory
• Examples
• Fred 10 integer
• Loop_count 0 integer
• User_name Carl Smith string
• NOTE Use a name that is relevant to its use

3
Declaration

• In Pascal, all variables must be declared before
  use. The variables are declared with the type of
  data they hold using the Var statement

4
Declaration cont

• Identifiers
• Identifiers are names that you use in your
  program for constants, types, variables,
  procedures, functions, units, programs and fields
  in records.
• They can contain letters(upper and lower cases),
  digits(0 to 9) and the underscore character but
  not spaces. The first character cannot be a digit
  and a name can be up to 63 characters long.
• Pascal identifiers are not case sensitive but
  must be unique within the program.

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Pascal Reserved Words
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DATA TYPES
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INTEGER Data Types

• Type From Through
• Byte 0 255
• Integer -32768 32767
• LongInt -2147483648 2147483647
• ShortInt -128 127
• Word 0 65535

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REAL Data Types

• Type Name Range of Values
• Comp 9.2E-18 to 9.2E18
• Double 5.OE-324 to 1.7E308
• Extended 3.4E-4932 to l.lE4932
• Real 2.9E-39 to 1.7E38
• Single 1.5E-45 to 3.4E48

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Declaration cont

• Strings are sequences of characters with a
  maximum size of 255 characters.String variables
  in particular can consume a lot of memory
• This can be reduced by declaring their length
  before use e.g.-
• fred string10
• Declares a string variable called fred that can
  contain up to ten characters

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Declaration cont

• You can declare the name, data type and length in
  one statement e.g.-
• Var
• namea, nameb, namec, named, namee, namef, nameg,
  nameh, namei, namej string20
• All the above variables become individual strings
  of length 20 characters each

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Constants

• When would you use a constant?
• A very good documented example comes from the
  NASA space centre.
• All programs controlling a launch use constants
  that store values such as wind speed,
  temperature, cloud cover etc. These are changed
  in the declaration section depending on the
  weather conditions to tailor the program to the
  prevailing conditions at lift off.

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Constants cont

• Examples-
• Pi 3.142
• Rulerline --------------------------
• VATrate 17.5
• Note that constants deduce the data type from the
  content

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Elements of a string variable

• String variables can be broken down into elements
  or individual characters
• We can think of itlooking like this -
• fred A Pascal Program
• Therefore fred3 P

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Introduction to Arrays

• We have seen that each character of a string
  variable can be addressed
• Arrays are a special kind of variable (of any
  data type) that have an Index number attached
  to each element such as-
• VarName1 or VarName10

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Declaration of arrays

• We declare arrays in the following way-
• ltvar identifiergt array range of lttypegt e.g.
• Var
• name array 1..10 of string20

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To Use

• We could input to or output any element of the
  array-
• readln(name5)
• writeln(Contents are , name5)
• Arrays come into their own when we use within
  an iterative loop

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To use (cont)

• For example, we could display the whole (name)
  array with-
• for counter 1 to 10 do
• begin
• write(Contents of ,counter)
• writeln( is ,namecounter)
• end

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Summary

• We looked at-
• What is a variable?
• What is a constant?
• Data types of variables
• String Elements
• An Introduction to Arrays and Loops
• Declaration and examples
• QUESTIONS?