title: What exactly does the "+=" operator do?
body: <p>I already know that <code>x += 1</code> means <code>x = x + 1</code>.
  The <code>=</code>-symbol allocates the value of the arithmetic expression on it's right to the variable on it's left.
  But if i have an expression like <code>x += y % 3</code>, does that mean <code>x = (x + y) % 3</code>or <code>x = x + (y % 3)</code>?
  The <code>+=</code> operator is both allocating a value to a variable and expressing arithmatics, which has me confused.</p>
  
  <p>Unfortunately I currently can't just test some code to check, so I hope I can get some help here.
  I'm new to C++, so some of these very basic things still confuse me...</p>