modula2 quick reference

Modula 2 Quick Syntax Reference

Beginners Version

Program Structure

MODULE ModuleName;

FROM IO IMPORT WrStr, WrLn; import general procedures

CONST PI = 3.1416; constante-declarations

VAR aNumber: CARDINAL; variabele-declarations

BEGIN
... statements
END ModuleName.

Single Types

CARDINAL
INTEGER
CHAR: characterconstant: 'a' (note the difference between the letter 'a' and the variable a)
REAL

conversion between cardinal <=> real:

real := FLOAT(cardinal);
cardinal := TRUNC(real); or use VAL(CARDINAL, real)

real constant format: -4.32E-3 (exponential part is optional)

real := 4; is illegal, this should be : real := 4.0;

BOOLEAN: values TRUE & FALSE, operators NOT, AND, OR

assignment: variable := value;
variables defined in the module (not in a procedure) are initialised with a 0.

Structured Types

ARRAY

variable declaration: VAR array1: ARRAY [1..20] OF CARDINAL;
element of array: array1[2] := 1;
special array: string (ARRAY OF CHARs)

assignment: str := "bla";
a 0 (not the letter '0') is placed in the array after the last character to indicate the end of the string.

multidimensional array :

VAR matrix10by20: ARRAY [1..10],[1..20] OF CARDINAL;
identical declaration: VAR matrix10by20: ARRAY [1..10], [1..20] OF CARDINAL;
use: matrix10by20[5, 15] := 7; or matrix10by20[5][15] := 7;

RECORD

declaration:

VAR jan : RECORD
name, firstName: ARRAY[1..35] OF CHAR;
length: CARDINAL;
END;

use: jan.name := "Lemeire"; jan.firstName := "Jan"; jan.length := 190;

record assignment is possible (rec1 := rec2;), but record comparison not (rec1 = rec2)!

for comparison: compare field by field: (rec1.a = rec2.a) AND (rec1.b = rec2.b)

Procedures

PROCEDURE MyFunction(inputVariable1, inputVariable2: CARDINAL; inputVariable3: WeekdayRc): BOOLEAN;
    VAR result: BOOLEAN;   variabele-declarations
BEGIN
    ...                  statements
    RETURN result;
END MyFunction;

2 types:

with returnvariable: RETURN value;

you may use multiple RETURN statements, but the procedure stops immediately after a return

without returnvariable

you may use RETURN; to quit the procedure.

resultVariable := MyFunction(cardinalVariable1, cardinalVariable2, mondayRc);
Local variables of a procedure are NOT initialised automatically!! They can have any value at start.
Scoop (variables, types & procedures): go out & up.

a procedure must thus be defined before it can be used.

Operators

NOT, AND, OR
=, # equals, different
+, -, *, /, MOD (modulo = rest), y := ABS(x)(absolute value, for integers & reals)
<, >, >=, <= relational operators

Use round brackets (haakjes) to indicate evaluation priorities
eg: IF x MOD 3 = 0 THEN gives an error (the = operation is evaluated before the MOD)
this should be: IF (x MOD 3) = 0 THEN

Control Statements

IF (a > 5) OR (b > 6) THEN     condition
    ...                      statements
ELSE                      optional
    ...                      statements
END;

WHILE NOT (i > 10) DO condition
statements...
END;

REPEAT
statements...
UNTIL (i = 10);

FOR i := 10 TO 0 BY -1 DO By clause is optional
statements...
END;

Library RealMath (mathematical functions on reals)

sqrt (x: REAL): REAL; Returns the positive square root of a positive x
power (base, exponent: REAL): REAL; Returns the value of the number base raised to the power exponent.

Warning: base may not be negative!! Use ABS(base) to make it positive.

Procedures (library IO) Take these to when using black window

WrLn; skip to next line
cardinalVariable := RdCard(); read cardinal
WrCard(cardinalVariable, spaces); write cardinal
readVariable := RdInt();
WrInt(intVariable, spaces);
RdStr(stringVariable); read string (variabele tussen de haakjes!!)
WrStr(stringVariable); write string to output
charVariable := RdKey(); reads a key, use this instead of RdChar()
charVariable := RdChar(); !! 2 ENTER-tokens stay in input buffer, are read in the next time with a RdChar

RdLn; use this after RdChar to read the rest of the input and the ENTER-tokens

WrChar(charVariable);
realVariable := RdReal(); read real from user input
WrReal(realVariable, precision, spaces); write real to output (precision: number of digits)
booleanVariable := RdBool(); ty pe "TRUE" and "FALSE"
WrBool(booleanVariable, spaces);

Procedures (library Graph)

Colours are defined as numbers from 0 to 15, or use the constants _clrBLACK, _clrBLUE, _clrGREEN, _clrCYAN, _clrRED, ...
Coordinates and colours are cardinals.

BOOLEAN Init(1, 1 , width, height); Creates graphical screen with, returns if OK
Plot(x, y, colour); Draws a coloured point at x,y
Line(x1, y1, x2, y2, colour); Draws a line from x1,y1 to x2,y2
Rectangle(x1, y1, x2, y2, colour, Filled); Rectangle between x1,y1 and x2,y2, filled is a boolean
Circle(x0, y0, radius, colour); Circle with center x0, y0 and radius
Disc(x0, y0, radius, colour); Disc is a filled circle
RawOutText(x0, y0, colour, text); Writes Text starting from x0,y0