I don't understand ruby local scope

Question

In this example,

def foo(x)
  if(x > 5)
    bar = 100
  end
  puts bar
end

Then foo(6) Outputs: 100 and foo(3) outputs nothing.

However if i changed the definition to

def foo(x)
  if(x > 5)
    bar = 100
  end
  puts bob
end

I get an "undefined local variable or method" error.

So my question is why I am not getting this error when I call foo(3) and bar is never set?

Answer

There a couple of things going on here. First, variables declared inside the if block have the same local scope as variables declared at the top level of the method, which is why bar is available outside the if. Second, you're getting that error because bob is being referenced straight out of the blue. The Ruby interpreter has never seen it and never seen it initialized before. It has, however, seen bar initialized before, inside the if statement. So when is gets to bar it knows it exists. Combine those two and that's your answer.