Learn MODULA3 with Real Code Examples

MODULE CounterTheme;

IMPORT IO;

VAR
    count: INTEGER := 0;
    isDark: BOOLEAN := FALSE;

PROCEDURE updateUI():=BEGIN
    IO.Put("Counter: "); IO.PutInt(count, 0); IO.PutLn();
    IF isDark THEN
        IO.PutLn("Theme: Dark")
    ELSE
        IO.PutLn("Theme: Light")
    END;
END updateUI;

PROCEDURE increment():=BEGIN
    count := count + 1;
    updateUI();
END increment;

PROCEDURE decrement():=BEGIN
    count := count - 1;
    updateUI();
END decrement;

PROCEDURE reset():=BEGIN
    count := 0;
    updateUI();
END reset;

PROCEDURE toggleTheme():=BEGIN
    isDark := NOT isDark;
    updateUI();
END toggleTheme;

BEGIN
    updateUI();
    increment();
    increment();
    toggleTheme();
    decrement();
    reset();
END CounterTheme.

Demonstrates a simple counter with theme toggling using Modula-3 variables, procedures, and safe I/O.

MODULE RandomGen;
IMPORT IO, SYSTEM;
VAR i, num: INTEGER;
BEGIN
    FOR i := 1 TO 3 DO
        num := SYSTEM.Random() MOD 100 + 1;
        IO.Put("Random "); IO.PutInt(i,0); IO.Put(" : "); IO.PutInt(num,0); IO.PutLn();
    END;
END RandomGen.

Generates random numbers between 1 and 100 and prints them.

MODULE TodoList;
IMPORT IO;
VAR todos: ARRAY [0..9] OF STRING;
VAR count: INTEGER := 0;

PROCEDURE addTask(task: STRING);
BEGIN
    todos[count] := task; count := count + 1;
    FOR i := 0 TO count-1 DO IO.PutLn(todos[i]) END;
END addTask;

PROCEDURE removeTask(index: INTEGER);
VAR i: INTEGER;
BEGIN
    FOR i := index TO count-2 DO todos[i] := todos[i+1] END;
    count := count - 1;
    FOR i := 0 TO count-1 DO IO.PutLn(todos[i]) END;
END removeTask;

BEGIN
    addTask("Buy milk");
    addTask("Write Modula-3 code");
    removeTask(0);
END TodoList.

Maintains a simple todo list with add and remove functionality.

MODULE DiceRoll;
IMPORT IO, SYSTEM;
VAR i, roll: INTEGER;
BEGIN
    FOR i := 1 TO 3 DO
        roll := SYSTEM.Random() MOD 6 + 1;
        IO.Put("Roll "); IO.PutInt(i,0); IO.Put(" : "); IO.PutInt(roll,0); IO.PutLn();
    END;
END DiceRoll.

Rolls a six-sided dice three times.

MODULE Countdown;
IMPORT IO;
VAR count: INTEGER := 5;
BEGIN
    WHILE count >= 0 DO
        IO.Put("Countdown: "); IO.PutInt(count,0); IO.PutLn();
        count := count - 1;
    END;
    IO.PutLn("Done!");
END Countdown.

Counts down from 5 to 0.

MODULE PrimeCheck;
IMPORT IO;
VAR nums: ARRAY [0..2] OF INTEGER := [7,10,13];
VAR n, i: INTEGER;
VAR isPrime: BOOLEAN;
BEGIN
    FOR n IN nums DO
        isPrime := TRUE;
        FOR i := 2 TO n-1 DO
        IF n MOD i = 0 THEN isPrime := FALSE END;
        END;
        IO.PutInt(n,0);
        IF isPrime THEN IO.PutLn(" is Prime") ELSE IO.PutLn(" is Not Prime") END;
    END;
END PrimeCheck.

Checks if numbers are prime.

MODULE TempConv;
IMPORT IO;

PROCEDURE cToF(c: REAL): REAL;
BEGIN RETURN c*9/5+32 END cToF;

PROCEDURE fToC(f: REAL): REAL;
BEGIN RETURN (f-32)*5/9 END fToC;

BEGIN
    IO.Put("25°C = "); IO.PutReal(cToF(25),2); IO.PutLn();
    IO.Put("77°F = "); IO.PutReal(fToC(77),2); IO.PutLn();
END TempConv.

Converts Celsius to Fahrenheit and Fahrenheit to Celsius.

MODULE ShoppingCart;
IMPORT IO;
VAR cart: ARRAY [0..9] OF STRING;
VAR prices: ARRAY [0..9] OF INTEGER;
VAR count: INTEGER := 0;

PROCEDURE addItem(item: STRING; price: INTEGER);
BEGIN
    cart[count] := item; prices[count] := price; count := count + 1;
    (* print cart and total sum here *)
END addItem;

PROCEDURE removeItem(index: INTEGER);
VAR i: INTEGER;
BEGIN
    FOR i := index TO count-2 DO cart[i] := cart[i+1]; prices[i] := prices[i+1] END;
    count := count -1;
    (* print cart and total sum here *)
END removeItem;

BEGIN
    addItem("Apple", 2);
    addItem("Banana", 3);
    removeItem(0);
END ShoppingCart.

Adds and removes items in a shopping cart with total cost.

MODULE Greet;
IMPORT IO;
PROCEDURE greet(name: STRING);
BEGIN
    IO.Put("Hello, "); IO.Put(name); IO.PutLn("! Welcome!");
END greet;

BEGIN
    greet("Saurav");
    greet("Alice");
    greet("Bob");
END Greet.

Greets users by name.

MODULE Stopwatch;
IMPORT IO;
VAR time: INTEGER := 0;
BEGIN
    WHILE time < 5 DO
        IO.Put("Stopwatch: "); IO.PutInt(time,0); IO.PutLn();
        time := time + 1;
    END;
    IO.PutLn("Done!");
END Stopwatch.

Simulates a stopwatch incrementing seconds.