Records. Records with variants. Operator with

1. What are the benefits of records in Pascal?

Records allow you to group different types of data on certain grounds. The fields of records may be variables of different types.

For example:

a record that contains information about the coordinates of point on the plane (x; y);
a record that contains information about name, surname and patronymic of worker;
a record that contains information about the book in library: name of reader, address of reader.

Using of records is the convenient way, when you need to save and process the arrays of variables of different types.

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2. What types of variables you may use in the records?

In the records variables can be different types. It can be and standard types of data and user data types. This significantly differs the record from array.

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3. What is the general view of record?

In the application you can define the record by two ways:

– by using a definition of record’s type in the section type;

– by using a definition of variable of record’s type in the section var.

Way 1. Record’s definition by using of section of type definition “type”. The result is a its own type, which is a record. With the help of this way it is possible to use the variables that are records in the procedures and functions as parameters.

type
  <Name_type_record> = record
    <field1:type>
    <field2:type>
    ...
    <fieldN:type>
  end;

where

Name_type_record – the name of type, which is assigned to the variables of this record;

field1, field2, fieldN – the names of variables which are the fields of record;

type – the name of some type from allowable types of program (integer, real, string …);

After this describing it is possible to define the variable of these type in the section var:

var
  <Variable_name>:<Name_type_record>;

Way 2. Definition of record immediately in the section var.

var
  <Variable_name>: record
    <field1:type>
    <field2:type>
    ...
    <fieldN:type>
  end;

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4. An example of definition and using the record, which describes the coordinates of point on the plane (x; y).

Way 1. By using the type section of type’s definition.

type
  // The 'TPoint' record definition
  TPoint = record
    x:real; // x coordinate
    y:real; // y coordinate
  end;

var
  P:TPoint; // variable named 'P' of TPoint type

To save the values of coordinates in the variable P, you need to write the following text:

...

begin

  ...

  P.x := 12.5;
  P.y := -8.3;

  ...

end;

...

Way 2. In the var section of variables definition.

var

P2:record // variable record has two fields x and y
     x:real;
     y:real;
   end;

To access to the fields of variable P2 you need to write following:

...

begin

  ...

  P2.x := -9.25;
  P2.y := 18;

  ...

end;

...

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5. An example of definition and using of record of type TBOOK.

An example of definition the record of TBOOK type that includes following fields:

the book’s title;
author’s name;
year of publication of the book;
the cost of the book.

type
  TBOOK = record
    Title:string;
    Author:string;
    Year:integer;
    Price:real;
  end;

var
  B:TBOOK;

...

begin

  ...

  B.Title := 'Java 8';
  B.Author := 'Herbert Schildt';
  B.Year := 2015;
  B.Price := 0.00;

  ...

end;

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6. How to assign one record to another record?

To assign the value of fields from one record to another record these records must be the same type. This type must be defined in the section type.

In the example below, the assignment between variables M1 and M2 is realized. Two variables are the records of type TMonth.

type
  // Definition of record that describes the month of the year
  TMonth = record
    num:1..12;       // the month in the year (1-january, 2-february, ...)
    name:string[20]; // the name of month
    quarter:1..4;   // number of quarter
  end;

var
  M3:record 
    num:1..12;   // the month in the year (1-january, 2-february, ...) 
    name:string[20]; // the name of month 
    quarter:1..4;   // number of quarter  
  end; 

  M1,M2:TMonth; 

begin 

  ...

  M1.num := 2; 
  M1.name := 'Февраль'; 
  M1.quarter := 1; 

  // assignment between records 
  M2:=M1; 

  // Error - Incompatible types: 'Record' and 'TMonth' 
  // M3:=M1;  

  ... 

end;

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7. An example of definition and using of one-dimensional array of records of type BOOK.

...

type

  TBOOK = record
    Title:string;
    Author:string;
    Year:integer;
    Price:real;
  end;

var
  Books:array[1..20] of TBOOK;

begin

  ...

  Books[3].Title := 'C# 4.0';
  Books[3].Author := 'Herbert Schildt';
  Books[3].Year := 2011;
  Books[3].Price := 0.99;

  ...

end;

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8. An example of definition and using the nested records.

In the example below two records of types TName and TBOOK are defined. In the record of TBOOK type, the variable of type TName is defined.

type
  TName = record
    Name:string[20];
    Surname:string[20];
  end;

  TBOOK = record
    Title:string;
    Author:TName; // nested record
    Year:integer;
    Price:real;
  end;

var
  Books:array[1..20] of TBOOK;
  B:TBOOK;

begin

  B.Title := 'C# 4.0';
  B.Author.Name := 'Herbert';
  B.Author.Surname := 'Schildt';
  B.Year := 2011;
  B.Price := 0.99;

end;

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9. What are the advantages of With operator in the records?

The “with” statement allows you to reduce the long notation of elements records. “with” statement also improves readability and reduces typing the text of the program in which there is frequent reference to the record fields. In addition, the with statement reduces the execution time of the program, because link to the record is carried out only once.

The “with” statement opens a scope that includes field names a variable of type “Record”.

The general form of “with” statement:

with <Variable_name> do
  statement;

The statement with can be composite:

with <Variable_name> do
begin
  statement1;
  statement2;
  ...
  statementN;
end;

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10. An example of using “with” statement.

type
  TName = record
    Name:string[20];
    Surname:string[20];
  end;

  TBOOK = record
    Title:string;
    Author:TName; // nested record
    Year:integer;
    Price:real;
  end;

var
  B:TBOOK;

begin

  with B do
  begin
    Title := 'C# 4.0';
    with Author do
    begin
      Author.Name := 'Herbert';
      Author.Surname := 'Schildt';
    end;
    Year := 2011;
    Price := 0.99;
  end;

end;

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11. What benefits of using the records with variants?

In records it is possible to set the type, that includes definitions of several options of structure.

The record with variants – this is the variable that can include objects of different types and sizes. Compiler performs all requirements for sizes and alignment. Records with variants allows you to save data in the memory.

A record may include only one part of variant (in the section “case“). If you use the variants parts in the program, it minimizes the memory allocation. It is effective in the program when you use the arrays of records that contain many fields.

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12. An example of using the variant’s record.

In the example below is the definition and using the variant’s record. This record describes whether the worker of the institution is in a particular category of workers.

According to category, the corresponding fields of worker are formed. The category of worker is saved in the variable f_worker.

type
  TName = record
    Name:string[20];
    Surname:string[20];
  end;

  // The record with variant, that describes of worker of institution
  TWorker = record
    name:TName; // Name of worker
    birth:string[10]; // birth date

    // The worker can be in the one of three categories
    case f_worker:1..3 of
      1: // if the administration
        (post_adm:string[100]; // position
         rate:real;   // rate: 0.5, 0.75, 1.0
         salary:real); // the salary

      2: // if the teacher
        (hours:integer;   // teaching load, hours
         fee: real);       // payment per hour

      3: // if support personnel
        (post_pers:string[100]; // name of position
         rank:integer;     // wage category
         tariff:real);       // tariff rate
  end;

var
  W1:TWorker;

begin

  W1.name.Name := 'Ivan';
  W1.name.Surname := 'Kornilenko';
  W1.birth := '19.02.1988';

  // If worker is administration then
  W1.f_worker := 1; // administration
  W1.post_adm := 'Director';
  W1.rate := 0.75;
  W1.salary := 18800.50;

  // If worker is a teacher then
  W1.f_worker := 2;
  W1.hours := 72;
  W1.fee := 230.55;

  // If worker is personnel then
  W1.f_worker := 3;
  W1.post_pers := 'Driver';
  W1.rank := 3;
  W1.tariff := 14390.35;

end;

The record with variants includes the “case…of” part. Compiler interprets the fields of record according to the value of variable f_worker.

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Pascal. Records