What's the difference between x<<a + x<<b with and without parenthesis

Question

I want to multiply a number by 10 using bit-shift operators.
To try, I initialized x = 1. Then I assigned x = x<<1 + x<<3.This printed x = 32.
But when I assigned x = (x<<1) + (x<<3), it printed x = 10.

Where does this difference come from?

I am using c++11.

Answer 1

Look at the difference :

x = x<<1 + x<<3
x = 1<<1 + 1<<3     // execute 1+1 first
x = 1<<2<<3         // execute 1<<2
x = 4<<3
x = 32

and this

x = (x<<1) + (x<<3)
x = (1<<1) + (1<<3)
x = 2 + 8
x = 10

Answer 2

The expressions in the parenthesis are being evaluated first. Without them, the shift operations are being performed before the addition.

First, C++ evaluates (x << 1) which equals 2.

Then it evaluates (x << 3) which equals 8.

Finally, it adds them 2 + 8 = 10.