Chapter 7
                                  STRINGS & STRING PROCEDURES


PASCAL STRINGS
____________________________________________________________

According to the Pascal definition, a        ================
string is simply an array of 2 of more         STRARRAY.PAS
elements of type char, and is contained in   ================
an array defined in a var declaration as a
fixed length.  Look at the example program
STRARRAY.PAS.  Notice that the strings are defined in the type
declaration even though they could have been defined in the
var part of the declaration.  This is to begin getting you
used to seeing the type declaration.  The strings defined here
are nothing more than arrays with char type variables.


A STRING IS AN ARRAY OF CHAR
____________________________________________________________

The interesting part of this file is the executable program. 
Notice that when the variable First_Name is assigned a value,
the value assigned to it must contain exactly 10 characters
or the compiler will generate an error.  Try editing out a
blank and you will get an invalid type error.  Pascal is neat
in allowing you to write out the values in the string array
without specifically writing each character in a loop as can
be seen in the Writeln statement.  To combine the data, called
concatenation, requires the use of the rather extensive
looping and subscripting seen in the last part of the program. 
It would be even messier if we were to consider variable
length fields which is nearly always the case in a real
program.

Two things should be observed in this program.  First, notice
the fact that the string operations are truly array operations
and will follow all of the characteristics discussed in the
last chapter.  Secondly, it is very obvious that Pascal is
rather weak when it comes to its handling of text type data. 
Pascal will handle text data, even though it may be difficult
to do so using the standard description of Pascal as
illustrated in this program.  We will see next that TURBO
Pascal really shines here.  Compile and run STRARRAY.PAS and
observe the output.


THE TURBO PASCAL STRING TYPE
____________________________________________________________

Look at the example program STRINGS.PAS.  You will see a much
more concise program that actually does more.  TURBO Pascal
has, as an extension to standard Pascal, the string type of

                                                     Page 7-1

                                Strings and String Procedures

variable.  It is used as shown, and the     =================
number in the square brackets in the var       STRINGS.PAS
declaration is the maximum length of the    =================
string.  In actual use in the program, the
variable can be used as any length from
zero characters up to the maximum given in the declaration. 
The variable First_Name, for example, actually has 11
locations of storage for its data.  The current length is
stored in First_Name[0] and the data is stored in
First_Name[1] through First_Name[10].  All data are stored as
byte variables, including the size, so the length is therefore
limited to a maximum of 255 characters.



STRINGS HAVE VARIABLE LENGTHS
____________________________________________________________

Now look at the program itself.  Even though the variable
First_Name is defined as 10 characters long, it is perfectly
legal to assign it a 4 character constant, with First_Name[0]
automatically set to 4 by the system and the last six
characters undefined and unneeded.  When the program is run
the three variables are printed out all squeezed together
indicating that the variables are indeed shorter than their
full size as defined in the var declaration.  

Using the string type is even easier when you desire to
combine several fields into one as can be seen in the
assignment to Full_Name.  Notice that there are even two
blanks, in the form of constant fields, inserted between the
component parts of the full name.  When it is written out, the
full name is formatted neatly and is easy to read.  Compile
and run STRINGS.PAS and observe the output.



WHAT'S IN A STRING TYPE VARIABLE?
____________________________________________________________

The next example program named               ================
WHATSTRG.PAS, is intended to show you          WHATSTRG.PAS
exactly what is in a string variable.        ================
This program is identical to the last
program except for some added statements
at the end.  Notice the assignment to Total.  The function
Length is available in TURBO Pascal to return the current
length of any string type variable.  It returns a byte type
variable with the value contained in the [0] position of the
variable.  We print out the number of characters in the string
at this point, and then print out each character on a line by
itself to illustrate that the TURBO Pascal string type
variable is simply an array variable.


                                                     Page 7-2

                                Strings and String Procedures

The TURBO Pascal reference manual has a full description of
several more procedures and functions for use with strings
which are available in TURBO Pascal only.  Refer to your TURBO
Pascal version 3.0 reference manual in chapter 9, beginning
on page 67, or if you are using TURBO Pascal version 4.0, you
will find the string functions throughout chapter 27.  The
TURBO Pascal Reference Guide for version 5.X has a list of
string procedures and functions on page 120.  The use of these
should be clear after you grasp the material covered here.


PROGRAMMING EXERCISE
____________________________________________________________

1.   Write a program in which you store your first, middle,
     and last names as variables, then display them one to a
     line.  Concatenate the names with blanks between them and
     display your full name as a single variable.





































                                                     Page 7-3