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Introduction To
the Pascal Language

In Lazarus

Lazarus Pascal - An Introduction

Lazarus is an implementation of EVENT DRIVEN Pascal for windows. It offers the programmer a rich collection of conventional Pascal operators, data types and control structures. In addition, Lazarus provides an extensive palette of VISUAL COMPONENTS, allowing for Rapid Application Development (RAD) with minimal coding.

If you have a version of Lazarus other than version 1, you can write Console Applications (Text-based applications) that feature many of the features of a CRT-based application without some of the CRT routines (like clrscr, gotoxy etc). If you are interested in doing this, then you can learn more about Console Applications for practising standard text-based Procedural Pascal.

General Features

  • the programs' data is as important as the instructions (equal weight of time will be devoted to each in this course)
  • all data used in programs is of distinct types (eg. integer, real, byte, boolean, char, string etc..)
  • there are rigid restrictions on how instructions can be written (syntax)
  • it is a small language (with a limited vocabulary of approx 40 reserved words), but capability only limited by skill of programmer
  • it is LOGICAL, requires sequential, modular approach to problem solving (learning this will drive you nuts).
  • it is COMPILED (ie. SOURCE code compiled into .EXE files in either memory, or on disk) which can then be run in Windows. The Compiler will identify SYNTAX errors, and only SOME LOGICAL ERRORS - it is the programmers job to construct a correct program (as compared with one that compiles OK but gives the wrong answers)

SYNTAX: rules for allowable statement formation (lines of code)

CONVENTION: established practices affecting the appearance, organisation and readability of a program (SHOULD be obeyed)

Shortcuts to reduce program size and speed up program are outside scope of this course (and fall into the topic of optimization or hacking). Rather we will aim for consistency, readability, problem solving skills and good programming skills that do not need to be hacked.

General Unit Outline:


    procedure procedurename; {Environment}

    uses libraryname, unitname; {included resources}

    var declarations {Store}

    begin

    statements {Body}

    end;

A Programs Environment:

A windows application is bathed in many layers of resources, including graphical resources central to the operating environment + functionality of the operating system + predefined data types + predefined constants (eg. pi) + reserved words + predefined routines (eg. input/output).

Programmers can add to this environment in any of the above areas with self written components.

Lazarus Identifiers (names for things)

Identifiers can be variable names, program names, procedure/function names, object names or names for properties and events associated with those objects


    SYNTAX: letter {letter | digit | underscore}

    NOTES: RESERVED words cannot be used as identifiers and an identifier must be <127 characters long

    EXAMPLES: V, A2_VARIABLE, a_long_variable

Lazarus IS NOT case specific i.e. a3 same as A3 for a name

CONVENTIONS:

  • use meaningful identifiers (AVOID single letters which tell nothing of the values they represent)
  • avoid very long identifiers - difficult to read and a pain in the **** to type.
  • use abbreviations for easy to recognise variables (eg. tot, Avg etc.)
  • for names containing multiple words, capitalise the first letter of each word LastVal
  • BE CONSISTENT, don't chop and change.

The Store

  • this is where the machine places data your program needs
  • you need to declare the TYPE of information (this defines how much memory space is needed to store it) and its' name (what name we are going to refer to the VALUE by, which is translated into a memory location).


SYNTAX: {Var identifier {,identifier} : type;
{identifier {,identifier} : type;}}


example:

Var

aNum, anotherNum : real;
total : integer;
answer : boolean;
ch : char;

Process Body


SYNTAX:

begin

[statement { ; statement } ]

end;

You should note that statements are SEPARATED by semi-colons (so the last statement in a program DOES NOT need one). It is possible but unusual (and wasteful of processor cycles) to have a empty (NULL) body. This is sometimes used for var checking with the compiler.

It is most common to begin each statement on a new line, aligned with statements at the same level process. It is generally NOT acceptable to 'stack' more than one statement on a line. If, however, the statements are very compact, and relate to each other, then this rule may be relaxed. Generally, however, this leads to less readible code, and is frowned upon.

Comments

Many beginning programmers (newbies) undervalue these (or worse, say they will add them later but never do). Comments are important 'notes' that programmers place in their programs indicating what the program does.

SYNTAX: [ { | (* [ text ] *) | } ]

EXAMPLES:
{ this is a comment }
(* this is also a comment *)
{ this is incorrectly formed *)

Comments are used to explain sections of code. They add nothing to OBJECT code, and do not make the EXE any bigger, so can use as many as we like. They are used to explain unusual methods employed. They can provide references and proofs of methods. The can identify overall purpose of program. They identify the programmer.

THEY ARE NOT OPTIONAL!

Comments if incorrectly applied can cause PROBLEMS.

An OPEN comment marker ({ or (*) causes to look for a matching CLOSE comment marker (} or *)) - once it finds one it trashes all in between when making OBJECT CODE (the EXE) - this can have the undesired effect of ditching code you want included.

eg.
{ this is a poorly placed comment *)
statement1;
statement2;
{ another comment here }
statement3;
statement4

The above code will cause statements 1 and 2 to be LEFT OUT of the OBJECT code at compile time. Can you see why?

Reserved Words

What follows is a list of some of the words that mean something specific in Lazarus - they cannot be used for anything other than their intended purpose.

at begin case const downto else end except finally for forward function if implementation initialization interface private procedure public raise repeat restrictions string try type unit until uses var while with

There are many other words known to Lazarus, and standard functions, procedures and constants, which can be used by a programmer or re-defined. Be warned, however, that re-defining an existing word in Lazarus effectively cancels out it's original purpose.

Introducing Lazarus Pascal Syntax
 

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