What's happening with this expression? b = a + (a = a + 5)

Question

a = 5
b = a + (a = a + 5)

result b = 15

Why the first \'a\' do not changes after that (a = a + 5)? But why second one changes? What exactly is

Answer 1

The expression is always evaluated from left to right & then assigned to whatever on left hand. As

  a = 5
  b = a + (a = a + 5)
\\b = 5 + (a = 5 + 5)
  b = 15