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pascal_cursus_1_en.md

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Pascal (1)

Koen asked me to write a course on PASCAL. And because I think PASCAL is a well structured and nice language I agreed.

Before I begin the real work (the course), I will do a short introduction. PASCAL (the language) is given the name of Blaise Pascal the mathematician who lived from 1623 till 1662. He was one of the great mathematicians that lived. He laid down the basics for calculating changes. One of his 'hobbies' was trying to create machines that did mathematics. He created a machine that could do various calculations (not only adding and subtracting) that was entirely mechanical (try to imagine this).

In about 1970 The name PASCAL (in capitals) was 'reintroduced'. Professor Niklaus Wirth though it nice to name his new programming language to the great mathematician. I think most people have heard or read about PASCAL. PASCAL has a lot of advantages compared to BASIC. PASCAL is almost self documenting because of its structure.

And now for the real thing. Lets begin with the structure of a PASCAL program:

PROGRAM program_name (INPUT,OUTPUT);

CONST {Constant definition}

TYPE {Type definition}

VAR {Variable declaration}

{Procedure and function definition}

BEGIN {Main program} END.

All words in capitals are reserved words. This means that this name cannot be used for something else (a variable for instance), they have a special function in a program. PROGRAM indicates that where about to make a PASCAL program. It is followed by the name of the program and the words INPUT and OUTPUT between brackets. The words INPUT and OUTPUT tell the compiler that the program uses standard in- and output (keyboard, screen). When working with files we will include more between the brackets.

After the program heading a block with constant, type and variable declaration follows. PASCAL forces you to declare all variables that you use in the program in advance. This not as in BASIC where you can declare a variable when you need it.

After this the procedure and function declarations follow. These declarations are equal to the 'program' declaration. In a later course we will handle this.

The last thing is a PASCAL program is the main program. The main program is enclosed by BEGIN and END.

That's it for the first course. I will leave you with a small and simple PASCAL program. Try to compile and run it and see if you can understand it.

 PROGRAM simple (INPUT,OUTPUT);

   VAR
     Value_1 : integer;
     Value_2 : integer;
     Result  : integer;

   PROCEDURE input_value(VAR value:integer);

     BEGIN          (* input_value *)
       Write('Input a value : ');
       Readln(value);
       Writeln;
     END;           (* input_value *)

   BEGIN            (* mainprogram *)
     Writeln('Example program for PASCAL-course (1)');
     Writeln('FutureDisk');
     Writeln;
     Writeln('Made by :');
     Writeln('Jeroen Smael');
     Writeln;
     Writeln;
     input_value(Value_1);
     input_value(Value_2);
     Result:=Value_1+Value_2;
     Writeln(Value_1:1,' + ',Value_2:1,' = ',Result:1);
     Writeln;
   END.             (* mainprogram *)

                              Jeroen 'PASCAL is fun' Smael