Pascal Programming

1
Pascal Programming

• Strings String Functions
• National Certificate Unit 4
• Carl Smith

2
What is a string?

• In a computer program a string is a variable
  length sequence of alpha-numeric characters.
• It can be used to store data typed in by a user
  or to present formatted data (information) to the
  user e.g.
• writeln(fred10)

3
Joining strings

• Strings often need to be concatenated or joined
  to make a further string
• In Pascal, this can be done in two ways-
• concat(string1.stringn)
• OR
• string3 string1 string2

4
String Functions

• length
• returns the length of a string
• writeln (length of string ,length(fred))

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Inserting strings

• insert
• inserts a string into another string at a fixed
  point
• insert(added, fred, 5)
• inserts the word added starting at 5th
  character of string fred

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Copy Function

• Copysometimes called (in VB for example) the
  substring, left or right
• It allows you to select part of an existing
  string e.g.
• fred Hello out there
• fred2 copy(fred, 7, 3)
• would make fred2 equal out

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Pos function

• Pos (sometimes called the index)
• returns the START position of a substring within
  a string
• fred Hello out there
• writeln(Position is ,pos(the,fred))
• returns the value of 11(NOTE a space is still a
  character)

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Delete Function

• Delete
• deletes a substring from a string
• fred Hello you out there
• delete(fred, 7 , 4)
• will delete you (including the space) from the
  string variable fred

9
Processing Strings

• We have the ability to address any character
  within a string
• remember that we can define a string with a
  maximum number of characters e.g.-
• fred string20
• fred1(fred1)fred1 contains 1st char
• fred2(fred2)fred2 contains the 2nd char
  etc
• NOTE that string fred is NOT an array, we are
  just accessing each one of the characters within
  the string using this technique.

10
Numbers and Strings

• Sometimes we need to convert a number stored in a
  string to an integer or real or vice versa
• Pascal provides the inbuilt STR and VAL
  procedures to allow this
• Val(ltstringgt,ltnumbergt,ltcodegt)ltnumbergt string
  converted to a number
• Str(ltnumbergt,ltstringgt)ltstringgt number
  converted to a string

11
Summary

• In this lecture we-
• Identified what a string is in a computer
  program
• Explored the functions that PASCAL provides to
  manipulate strings
• Looked at how to process strings