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Reserved WordsIdentifiersOperatorsStructures: Program, Branch, Loop

Pascal, udviklet af Niklaus Wirth 1968-70, blev i 1973 defineret med følgende reserverede ord og standard identifiers - beskrevet i bogen:
Kathleen Jensen & Niklaus Wirth: Pascal - User Manual and Report [Springer-Verlag 1975]

Reserved words

And, Array, Begin, Case, Const, Div, Do, Downto, Else, End, File, For, Function, Goto, If, In, Label, Mod, Nil, Not, Of, Or, Packed, Procedure, Program, Record, Repeat, Set, Then, To, Type, Until, Var, While, With

Standard Identifiers

Identifiers must start with a letter.
The predefined standard identifiers may be redifined (not that it is a good idea).

Constants

false, true, maxint

Types

integer, boolean, real, char, text

Functions

abs, arctan, chr, cos, eof, eoln, exp, ln, odd, ord, pred, round, sin, sqr, sqrt, succ, trunc

Procedures

get, new, pack, page, put, read, readln, reset, rewrite, unpack, write, writeln

Program Structure
v Minimal program: Hello World

program programname;
const
  const1 = value;
var
  var1: type;
label
  label1, label2;
  
procedure pname(param1: type, param2: type)
begin
  { statements }
end;
  
function fname(param1: type, param2: type): type
begin
  { statements }
  fname := value;  { function return value }
end;
  
begin
  { statements: program execution starts here }

label1: 

  goto label1;
end.

Program example:

program example;
const
  pi = 3.1416; 

  sep = '---------';
var
  radius, height : real;
  count : integer;
label
  1, 2;
  
function surface(r: real, h: real): real
var disk, cyl : real;

begin
  disk := pi * r * r;

  cyl : h * r;

  surface := 2 * disk + cyl;
end;
  
procedure line(str : array [] of char)
begin
  writeline(sep, ' ', str, ' ', sep);
end;
  
begin
  line ('start')

  count := 0; height := 5;

  writeline('Height: ', height);
1: 
  if count = 10 goto 2;

  count := count + 1;

  write('Radius: ', count);
  writeline(' - Surface area: ', surface(count, height));
  goto 1;

2:

  line ('End')
end.

Minimal program: 'Hello World':

program hello;
begin
  writeln('Hello World');
end.

Structure: Branch, Loop
> Program structure: Goto

If

x

Case

x

For

x

Repeat

x

While

x

Constants

false, true

false < true

>Types: boolean
>Operators: And, Or, Not

maxint

= 32767 in PC systems

Types

integer

>Operators: Div, Mod
>Functions: round, trunc

boolean

>Constants: false, true
>Operators: And, Or, Not, In, relational
>Functions: odd, eof, eoln

real

>Functions: sin, cos, arctan, ln, exp, sqrt

char

'a'..'z', 'A'..'Z', '0'..'9', ' ', '*', etc
>Functions: Chr, Ord

text

Operators

+, -, *, /

=, <>, <, >, <=, >= { relational operators }

>Types: boolean

in

>Types: boolean

And, Or, Not

>Types: boolean

Div, Mod

Div : Divide & Truncate
Mod: Division remainder

q := 27 Div 10 { q = 2 } r := 27 Mod 10 { r = 7 }

>Types: integer

Functions

abs (x)

The absolute value of x

 

arctan (x) : real

 

chr (x: integer) : char

>Ord

 

cos (x) : real

>Sin

 

eof (f: file) : boolean

end-of-file

 

eoln (f: file) : boolean

end-of-line

 

exp (x) : real

 

ln (x) : real

 

odd (x: integer) : boolean

True if x = 1, 3, 5, etc

 

ord (x: char) : integer

>Chr

 

pred (x: integer | char)

i := pred(5)   { i = 4 } c := pred('c') { c = 'b')

>succ

 

round (x: real) : integer

x rounded

i := round( 2.7)  { i =  3 } i := round(-2.7)  { i = -3 }

>trunc

 

sin (x) : real

>Cos

 

sqr (x)

x squared (x * x)

 

sqrt (x) : real

The square root of x

 

succ (x: integer | char)

i := succ(5)   { i = 6 } c := succ('c') { c = 'd')

>pred

 

trunc (x: real) : integer

x truncated (the whole part)

i := trunc( 2.7)  { i =  2 } i := trunc(-2.7)  { i = -2 }

>round

Procedures

get

new

pack

page

put

read

readln

reset

rewrite

unpack

write

writeln