Precedence rules

Precedence rules in C3 differs from C/C++. Here are all precedence levels in C3, listed from highest (1) to lowest (11):

  1. (), [], ., postfix ++ and --
  2. @, prefix -, prefix -%, ~, prefix *, &, prefix ++ and --
  3. infix *, /, %, *%
  4. <<, >>
  5. ^, |, infix &
  6. +, +%, infix -, infix -%
  7. ==, !=, >=, <=, >, <
  8. &&
  9. ||
  10. ternary ?:
  11. =, *=, /=, %=, +=, -=, <<=, >>=, &=, ^=, |=

The main difference is that bitwise operations and shift has higher precedence than addition/subtraction and multiplication/division in C3. 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   // C3 (>> is evaluated before + -)


a & b == c

a & (b == c)       // C  (bitwise operators are evaluated after relational)
(a & b) == c       // C3 (bitwise operators are evaluated before relational)


a > b == c < d

(a > b) == (c < d) // C  (< > binds tighter than ==)
((a > b) == c) < d // C3 Error, requires parenthesis!


a | b ^ c & d

a | ((b ^ c) & d)  // C  (All bitwise operators have different precedence)
((a | b) ^ c) & d  // C3 Error, requires parenthesis!

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 relational and equality operations, and all bitwise operations was motivated by simplification: few remember the exact internal differences in precedence between bitwise operators. Parenthesis are required for those conflated levels of precedence.

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.