Learn EIFFEL with Real Code Examples

class
    COUNTER
feature
    count: INTEGER
    is_dark: BOOLEAN

    update_ui
        do
        io.put_string ("Counter: " + count.out + '\n')
        io.put_string ("Theme: " + (if is_dark then "Dark" else "Light") + '\n')
        end

    increment
        do
        count := count + 1
        update_ui
        end

    decrement
        do
        count := count - 1
        update_ui
        end

    reset
        do
        count := 0
        update_ui
        end

    toggle_theme
        do
        is_dark := not is_dark
        update_ui
        end
end

! Simulate actions
local
    c: COUNTER
do
    create c
    c.update_ui
    c.increment
    c.increment
    c.toggle_theme
    c.decrement
    c.reset
end

Demonstrates a simple counter with theme toggling using Eiffel classes and methods.

class
    FIBONACCI
feature
    compute
        do
        local a, b, c, i: INTEGER
        a := 0
        b := 1
        io.put_integer(a); io.put_new_line
        io.put_integer(b); io.put_new_line
        from i := 1 until i > 8 loop
        c := a + b
        io.put_integer(c); io.put_new_line
        a := b
        b := c
        i := i + 1
        end
        end
end

! Run
local
    f: FIBONACCI
do
    create f
    f.compute
end

Generates first 10 Fibonacci numbers.

class
    FACTORIAL
feature
    compute (n: INTEGER)
        local f, i: INTEGER
        do
        f := 1
        from i := 1 until i > n loop
        f := f * i
        i := i + 1
        end
        io.put_string ("Factorial: "); io.put_integer(f); io.put_new_line
        end
end

! Run
local
    fact: FACTORIAL
do
    create fact
    fact.compute(5)
end

Calculates factorial of a given number.

class
    PRIME_CHECKER
feature
    is_prime (n: INTEGER): BOOLEAN
        local i: INTEGER
        do
        from i := 2 until i >= n loop
        if n \ i = 0 then
        Result := False
        return
        end
        i := i + 1
        end
        Result := True
        end
end

! Run
local
    p: PRIME_CHECKER
    num: INTEGER
do
    num := 13
    create p
    if p.is_prime(num) then
        io.put_string ("Prime"); io.put_new_line
    else
        io.put_string ("Not Prime"); io.put_new_line
    end
end

Checks if a number is prime.

class
    ARRAY_SUM
feature
    sum_array (arr: ARRAY[INTEGER])
        local total, i: INTEGER
        do
        total := 0
        from i := arr.lower until i > arr.upper loop
        total := total + arr[i]
        i := i + 1
        end
        io.put_string ("Sum: "); io.put_integer(total); io.put_new_line
        end
end

! Run
local
    a: ARRAY_SUM
    arr: ARRAY[INTEGER]
    i: INTEGER
do
    create a
    create arr.make(1,5)
    arr[1] := 1; arr[2] := 2; arr[3] := 3; arr[4] := 4; arr[5] := 5
    a.sum_array(arr)
end

Calculates the sum of an array of integers.

class
    REVERSE_STRING
feature
    reverse (s: STRING)
        local i: INTEGER; result: STRING
        do
        create result.make_empty
        from i := s.count until i = 0 loop
        result.append_character(s[i])
        i := i - 1
        end
        io.put_string(result); io.put_new_line
        end
end

! Run
local
    r: REVERSE_STRING
    s: STRING
do
    create r
    s := "Hello"
    r.reverse(s)
end

Reverses a string.

class
    MULT_TABLE
feature
    print_table (n: INTEGER)
        local i: INTEGER
        do
        from i := 1 until i > 10 loop
        io.put_integer(n); io.put_string (" x "); io.put_integer(i); io.put_string (" = "); io.put_integer(n * i); io.put_new_line
        i := i + 1
        end
        end
end

! Run
local
    t: MULT_TABLE
do
    create t
    t.print_table(5)
end

Prints the multiplication table of a number.

class
    TEMP_CONVERTER
feature
    c_to_f (c: REAL)
        local f: REAL
        do
        f := (c * 9.0 / 5.0) + 32.0
        io.put_real(f); io.put_new_line
        end
end

! Run
local
    t: TEMP_CONVERTER
do
    create t
    t.c_to_f(25.0)
end

Converts Celsius to Fahrenheit.

class
    ALARM_SIMULATION
feature
    check_temperature (temp, threshold: INTEGER)
        do
        if temp > threshold then
        io.put_string("Alarm: Temperature Too High!"); io.put_new_line
        else
        io.put_string("Temperature Normal"); io.put_new_line
        end
        end
end

! Run
local
    a: ALARM_SIMULATION
do
    create a
    a.check_temperature(80, 75)
end

Simulates a simple alarm when a threshold is reached.

class
    RANDOM_WALK
feature
    simulate (steps: INTEGER)
        local i, position: INTEGER
        do
        position := 0
        from i := 1 until i > steps loop
        if random(2) = 0 then
        position := position + 1
        else
        position := position - 1
        end
        io.put_integer(position); io.put_new_line
        i := i + 1
        end
        end
end

! Run
local
    rw: RANDOM_WALK
do
    create rw
    rw.simulate(10)
end

Simulates a random walk using integers.