Operator precedence
Precedence rules in C2 are different from C/C++. Here are all precedence levels in C2, listed from highest (1) to lowest (11):
(),[],., postfix++and--- prefix
-,~, prefix*,&, prefix++and-- - infix
*,/,% <<,>>^,|, infix&+, infix-==,!=,>=,<=,>,<&&,||- ternary
?: =,*=,/=,%=,+=,-=,<<=,>>=,&=,^=,|=,
The main difference is that bitwise operations and shift has higher precedence than addition/subtraction and multiplication/division in C2. Bitwise operations also have higher precedence than the relational operators. Also, there is no difference in precedence between && || or between the bitwise operators.
Examples
a + b >> c + d
(a + b) >> (c + d) // C (+ - are evaluated before >>)
a + (b >> c) + d // C2 (>> is evaluated before + -)
a & b == c
a & (b == c) // C (bitwise operators are evaluated after relational)
(a & b) == c // C2 (bitwise operators are evaluated before relational)
a || b && c
a || (b && c) // C (&& binds tighter than ||)
(a || b) && c // C2 (Same precedence, left-to-right evaluation)
a > b == c < d
(a > b) == (c < d) // C (< > binds tighter than ==)
((a > b) == c) < d // C2 (Same precedence, left-to-right evaluation)
a | b ^ c & d
a | ((b ^ c) & d) // C (All bitwise operators have different precedence)
((a | b) ^ c) & d // C2 (Same precedence, left-to-right evaluation)
The change in precedence of the bitwise operators corrects a long standing issue in the C specification. The change in precedence for shift operations goes towards making the precedence less surprising.
Conflating the precedence of || and &&, relational and equality operations, and all bitwise operations was motivated by simplification: few remember the exact internal differences in precedence between bitwise operators.
Left-to-right offers a very simple model to think about the internal order of operations, and encourages use of explicit ordering, as best practice in C is to use parentheses anyway.