For loops

Explanation

In the provided code snippet, there's a common misconception about how the variable i is being modified within the loop. Let me break it down for you:

i = 42

for i in (1...10)
  puts i
end

i # => 9

At first glance, it might seem like the variable i should retain its initial value of 42 since it's defined outside the loop.

However, in Ruby, the for...in loop doesn't create a new scope for the loop variable i.

Instead, it reuses the existing variable i defined outside the loop, effectively modifying its value.

Here's a step-by-step explanation of what happens:

1. i is initialized with the value 42.
2. The for...in loop iterates over the range (1...10), which includes integers from 1 to 9 (inclusive).
3. During each iteration of the loop, the loop variable i takes on the value of the current element in the range (1...10). So, i is successively assigned the values 1, 2, 3, ..., 9.
4. After the loop completes, the value of i is 9, which is the last value assigned to it within the loop.

Therefore, when you print the value of i after the loop (i # => 9), it reflects the final value assigned to i within the loop.

Here's a more explicit example to demonstrate the behavior:

i = 42

for j in (1...10)
  puts "j = #{j}, i = #{i}"
  i = j * 2
end

puts "Outside loop: i = #{i}"

This will output:

j = 1, i = 42
j = 2, i = 2
j = 3, i = 4
j = 4, i = 6
j = 5, i = 8
j = 6, i = 10
j = 7, i = 12
j = 8, i = 14
j = 9, i = 16
Outside loop: i = 16

As you can see, the value of i is modified within the loop and retains its final value (16) after the loop completes.

Voilà!