TOPIC I: VAL/VAR

Exercises :

(D1) VAR-demo.

(S1) Reset procedure

(S2) Your own version of INC

(S3) SWAP procedure.

(S4) DIV & MOD

(S5)

(X1)

(H1)

(H2)

(T1) Output

Verschil tussen Call by Value/Reference

D1: VAR-demo.

study the demo: parameters are changed IN the procedure.

S1: Reset procedures

Giving variables zero as a value is something that has to be done quite frequently. Write a procedure that takes an INTEGER as parameter and sets it to zero. Call this procedure zero. Example zero(x);
Make a more generic procedure which can assign arbitrary values to a variable. This procedure has 2 parameters: the variable whose value has to be set and a the value. Call this procedure set. You should be able to make zero using set but not the opposite... Example set(x, -99);

S2: Your own version of INC

Modula2 has a built-in INC procedure which is quite flexible. Make a procedure that does the same but only for CARDINALs. Call it myINC.

S3: Swap procedure

Make a procedure Swap that 'swaps' (verwisselen) two cardinals: x becomes y and vice versa.

VAR x, y: CARDINAL;
BEGIN
x := 7;
y := 10;
Swap(x, y);
WrStr(" x = ");WrCard(x, 0);WrLn;
WrStr(" y = ");WrCard(y, 0);WrLn;
END S3;

S4: DIV & MOD

Make a procedure that returns both the division (deling) and the modulo (rest) of two cardinals.

S5:

X1:

H1:

H2:

T1: Output

What is the output of the following program?

MODULE T1;
FROM IO IMPORT WrLn, WrCard, RdCard;

PROCEDURE proc1(VAR a1:CARDINAL; a2: CARDINAL):CARDINAL;
BEGIN
    a1 := a2 + 7;
    a2 := a2 - 7;
    RETURN a1 * a2 - 4;
END proc1;

PROCEDURE proc2(b1: CARDINAL; VAR b2:CARDINAL):BOOLEAN;
    VAR toReturn: BOOLEAN;
    b3:CARDINAL;
BEGIN
    b3 := b2;
    b2 := b1 MOD b3;
    b1 := b1 / b3;
    IF (b3 = 0) THEN
        toReturn := TRUE;
    ELSE
        toReturn := FALSE;
    END;
    RETURN toReturn;
END proc2;

VAR x1, x2, x3: CARDINAL;
BEGIN
    x1 := 3;
    x2 := 11;
    x3 := proc1(x1, x2);
    IF proc2(x3, x2) THEN
        x1 := x3;
    ELSE
        x1 := x2;
    END;

    WrCard(x1, 0);
    WrLn();
    WrCard(x2, 0);
    WrLn();
    WrCard(x3, 0);
    WrLn();
END T1.