1. (c)opyright Brent M. Dingle 2001
Pascal Records
Brent M. Dingle Texas A&M University
Chapter 11 – Section 1
(and some from Mastering Turbo Pascal 5.5, 3rd Edition by Tom Swan)
Fall 2001
(c)opyright Brent M. Dingle 2001

2. Record Types - Motivation
So far our only structured data type has been arrays.
A difficulty of arrays is they only allow the SAME data type to be stored within them.
What if we wanted to store a bunch of DIFFERENT data types together?
Do we really want to use a bunch of parallel arrays?
Fall 2001
(c)opyright Brent M. Dingle 2001

3. (c)opyright Brent M. Dingle 2001
Consider the problem:
We want to read in a bunch of information about many students and we want it all organized by name (or id number).
So the information on each student is:
Student Name
Student ID Number
5 Quiz Grades
3 Test Grades
7 Lab Grades
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(c)opyright Brent M. Dingle 2001

4. How would we store all that?
Currently we would need to make 5 different (parallel) arrays:
VAR
Name : array [1..NUM_STUDS] of string;
ID : array [1..NUM_STUDS] of string;
Quizzes : [1..NUM_STUDS][1..5] of real;
Tests : [1..NUM_STUDS][1..3] of real;
Labs : [1..NUM_STUDS][1..7] of real;
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5. (c)opyright Brent M. Dingle 2001
Organizing it
Then once we had all those arrays initialized properly,
We would have to sort the arrays by name (or id) and maintain the order of all of them.
This is extremely prone to error.
There must be an easier way.
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6. (c)opyright Brent M. Dingle 2001
Easier with Records
Fortunately Pascal allows us to do this in a much easier fashion.
We get to use Records.
But let’s look at a really simple case to illustrate all this.
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7. (c)opyright Brent M. Dingle 2001
Simple student info
Let’s reduce the student information to be just:
Student Name
Student ID
Student Grade
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8. (c)opyright Brent M. Dingle 2001
To store ONE student
We would need the following declarations:
TYPE
NAME_TYPE = string[40];
ID_TYPE = string[9];
GRADE_TYPE = real;
VAR
name : NAME_TYPE;
id : ID_TYPE;
grade : GRADE_TYPE;
Notice we use THREE variables.
Fall 2001
(c)opyright Brent M. Dingle 2001

9. Using records to store ONE student
We would need the following declarations:
TYPE
NAME_TYPE = string[40];
ID_TYPE = string[9];
GRADE_TYPE = real;
STUD_TYPE = RECORD
name : NAME_TYPE;
id : ID_TYPE;
grade : GRADE_TYPE;
END;
VAR
stud : STUD_TYPE;
Notice we use ONE variable.
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10. (c)opyright Brent M. Dingle 2001
And if we had 100 students
So if we had more than one student we would need
to make parallel arrays based on the above.
to make an array of the above record type
Compare the following
Fall 2001
(c)opyright Brent M. Dingle 2001

11. Using parallel arrays we would have the following
CONST
NUM_STUDS = 100;
TYPE
NAME_TYPE = string[40];
ID_TYPE = string[9];
GRADE_TYPE = real;
NAME_ARRAY = array[1..NUM_STUDS] of NAME_TYPE;
ID_ARRAY = array[1..NUM_STUDS] of ID_TYPE;
GRADE_ARRAY = array[1..NUM_STUDS] of GRADE_TYPE;
VAR
name : NAME_ARRAY;
id : ID_ARRAY;
grade : GRADE_ARRAY;
Fall 2001
(c)opyright Brent M. Dingle 2001

12. Initializing using parallel arrays
BEGIN { main }
for i:=1 to NUM_STUDS do
Begin
Input name[i]
Input id[i]
Input grade[i]
End
END.
Fall 2001
(c)opyright Brent M. Dingle 2001

13. Passing student data using parallel arrays
To pass the information on a student to a function or procedure we would need to send at least 3 parameters
e.g. ProcMisc(name, id, grade);
And hope the procedure would operate correctly on all 3 parameters using the correct indices.
It would be nice if we could just send ONE parameter.
Fall 2001
(c)opyright Brent M. Dingle 2001

14. Using records we would have the following
CONST
NUM_STUDS = 100;
TYPE
NAME_TYPE = string[40];
ID_TYPE = string[9];
GRADE_TYPE = real;
STUD_TYPE = RECORD
name : NAME_TYPE;
id : ID_TYPE;
grade : GRADE_TYPE;
END;
STUD_ARRAY = array [1..NUM_STUDS] of STUD_TYPE;
VAR
stud : STUD_ARRAY;
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(c)opyright Brent M. Dingle 2001

15. (c)opyright Brent M. Dingle 2001
Record Appearance
The above declarations look similar to those used for parallel arrays,
But look closely we added a bizarre line: STUD_TYPE = RECORD…
And we have only ONE array (of STUD_TYPE) declared.
Fall 2001
(c)opyright Brent M. Dingle 2001

16. Initializing - Using records
We could say:
BEGIN { main }
for i:=1 to NUM_STUDS do
Begin
Input stud[i].name
Input stud[i].id
Input stud[i].grade
End;
END.
Or we could simplify and say:
Input stud[i]
Fall 2001
(c)opyright Brent M. Dingle 2001

17. Passing student data using records
To pass the information on a student to a function or procedure we would need to only send ONE parameter
e.g. ProcMisc(stud);
Which is much easier (and ‘safer’) than sending three.
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18. (c)opyright Brent M. Dingle 2001
Too see more examples
Check out the code posted on the web to see a full working example using parallel arrays.
Contrast that with the example using a record type.
These example programs (or similar) will be presented in class.
Fall 2001
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19. (c)opyright Brent M. Dingle 2001
Important Side Note
Arrays are STILL said to only be of ONE data type,
They are of ONE record type.
The records may contain multiple types, but the array is still only of ONE record type.
So if asked how many types an array can contain the correct answer is ONE.
Fall 2001
(c)opyright Brent M. Dingle 2001

20. Definitions (from the book)
Know the definitions presented in the book.
Some, but not necessarily all, are listed below.
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21. (c)opyright Brent M. Dingle 2001
Fields
Fields, components, or component fields all refer to the same thing when talking about records.
Fields are the individual components of a record.
Example: In the STUD_TYPE above there are 3 fields.
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22. (c)opyright Brent M. Dingle 2001
Field Identifiers
Each field has a name, often called the field identifier.
Example: The 3 fields in STUD_TYPE above are:
name id
grade
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23. (c)opyright Brent M. Dingle 2001
Record Variable
A variable declared as a record type is referred to as a record variable.
Example:
VAR
student : STUD_TYPE;
Where STUD_TYPE was declared as above.
student is declared as a record type, thus student is a record variable.
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24. (c)opyright Brent M. Dingle 2001
Component Variable
A variable of a component of a record is called a component variable.
Example:
Let the variable student be a variable of record type STUD_TYPE
i.e. VAR student : STUD_TYPE;
Notice, STUD_TYPE has field identifiers name, id, and grade then the following are component variables:
student.name
student.id
student.grade
Fall 2001
(c)opyright Brent M. Dingle 2001

25. Record Syntax/Structure
Record types are declared in the TYPE section as follows:
TYPE
[record name] = RECORD
[field 1] : [type 1];
[field 2] : [type 2];
[field 3] : [type 3];
: :
[field n] : [type n];
END;
Fall 2001
(c)opyright Brent M. Dingle 2001

26. Records within Records
You may have a record type which contains a field that is of another record type.
Example:
TYPE
GRADE_REC = RECORD
grade : real;
letter: char;
END;
STUD_REC = RECORD
name : string[30];
grade : GRADE_REC;
Fall 2001
(c)opyright Brent M. Dingle 2001

27. With statement and Variant Records
For now don’t worry about using the WITH statement (if we get to it, then we get to it, if not then not =)
Regardless you will NOT need to know about variant records.
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(c)opyright Brent M. Dingle 2001

28. (c)opyright Brent M. Dingle 2001
Suggested Problems
pages 412, 413
1, 2, 4
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29. (c)opyright Brent M. Dingle 2001
End Pascal Record
Fall 2001
(c)opyright Brent M. Dingle 2001