<?php
// Initialize a variable $i with a value of 0
$i = 0;

// Use a while loop to execute the code block as long as the condition $i < 10 is true
while ($i < 10) {
    // Output the value of $i and add a new line
    echo $i . "\n";
    // Increment the value of $i by 1
    $i++;
}

// Use a do-while loop to execute the code block at least once before checking the condition
do {
    // Output a string
    echo "This will always be executed at least once\n";
// Set the condition to false, so the loop will only execute once
} while (false);

# The for keyword is used for loops that execute a block of code a certain number of times or until a condition is true
# The foreach keyword is used for iterating over arrays and hashes

# Example using both keywords:

# Loop that executes a block of code 10 times
for (my $i = 0; $i < 10; $i++) {
    print "$i\n"; # Prints the value of $i on a new line
}

# Loop that iterates over an array of colors
foreach my $color (@colors) {
    print "The color is: $color\n"; # Prints the value of $color with a descriptive message on a new line
}

# This script uses the for and while keywords to demonstrate their functionality in Python.

# The for keyword is used to iterate over a sequence, in this case, the range of numbers from 0 to 9.
# The variable i is used to store each value in the range as it loops through.
for i in range(10):
    print(i) # This line prints the current value of i.

# The while keyword is used to execute a block of code repeatedly until a condition is met.
# In this case, the condition is always True, so the loop will continue indefinitely until the user enters 'exit'.
while True:
    # The input() function prompts the user to enter a value, which is then stored in the variable num.
    num = input("Enter a number (or type 'exit' to quit): ")
    # The if statement checks if the user entered 'exit'.
    if num == 'exit':
        # If the condition is met, the break keyword is used to exit the loop.
        break
    else:
        # If the user did not enter 'exit', the else statement is executed.
        # The int() function converts the user's input into an integer.
        # The print() function then multiplies the integer by 2 and prints the result.
        print(int(num) * 2)

; The for keyword is used to iterate over a sequence or range of numbers.
; In this case, we are using it to iterate from 1 to 10.
for i 1 10 [
    ; The print function is used to output the value of i.
    print i
]

; The do keyword is used to execute a block of code repeatedly until a condition is true.
; In this case, we are using it to execute the block forever.
do forever [
    ; The if function checks if the condition is true.
    ; In this case, we are checking if the print function returns a value.
    if not (print "This will always be executed at least once")
    ; The do keyword is used to execute the break function, which exits the loop.
    do break
]

# This script uses the for and while keywords in Ruby to iterate over an array and execute a block of code repeatedly until a condition is met.

# First, we define a for loop to iterate over the range of numbers from 0 to 9.
for i in 0..9 do 
  # Within the loop, we use the puts method to print each number to the console.
  puts i
end

# Next, we define a while loop to execute a block of code repeatedly until a condition is met.
while true
  # We use the gets method to prompt the user for input and the chomp method to remove any trailing whitespace.
  num = gets.chomp.to_i
  # We use an if statement to check if the user input is equal to the string 'exit'.
  if num == 'exit'
    # If the condition is true, we use the break keyword to exit the loop.
    break
  else
    # If the condition is false, we use the print method to multiply the user input by 2 and print the result to the console.
    print(num * 2)
  end
end

# Overall, this script demonstrates how to use the for and while keywords in Ruby to iterate over an array and execute a block of code repeatedly until a condition is met.

(*
In Standard ML, we have the for and while keywords as well (surprise!). 
The for keyword is used for iterating over lists or ranges of numbers, 
whereas the while keyword is used for executing a block of code repeatedly 
until a condition is true. 
*)

(*
Here's an example using both:
*)

(*
The for keyword is used to iterate over a range of numbers from 1 to 10, 
and the print function is used to display the current value of i.
*)
for i = 1 to 10 do print(i)

(*
The while keyword is used to execute a block of code repeatedly until a 
condition is true. In this case, the condition is always true, so the code 
will continue to execute indefinitely.
*)
while true do (
    (*
    The val keyword is used to declare a variable named input, which will 
    hold the value of the user's input from the command line.
    *)
    val input = Sys.stdin.readLine() in
    (*
    The if statement checks if the user's input contains the word "exit". 
    If it does, the break keyword is used to exit the loop. Otherwise, the 
    code inside the else block will be executed.
    *)
    if String.isSubstring("exit", input) then break else (
        (*
        The let keyword is used to declare a variable named num, which will 
        hold the parsed integer value of the user's input.
        *)
        let num = Int.parse(input);
        (*
        The println function is used to display the result of multiplying 
        the user's input by 2.
        *)
        println(num * 2)
    )
)

'For' loop to iterate over numbers 0 to 9
For i = 0 To 9
    'Print the current value of i
    Console.WriteLine(i)
Next

'Do' loop to repeatedly execute a block of code until a condition is met
Do While True
    'Prompt user for input and convert it to an integer
    Dim input As Integer = CInt(Console.ReadLine())
    'Check if input is equal to "exit"
    If input = "exit" Then
        'Exit the loop if condition is met
        Exit Do
    End If
    'Print the result of input multiplied by 2
    Console.WriteLine("The result is: {0}", input * 2)
Loop