[面試題]C符號的優先順序

• int x = 0;
  if (x = 0 || x == 0) printf("%dn", x);
  printf("%dn", x);　　

• 參考C的優先表, 其實就是if (x = (0 || x == 0))
  會printf出兩個1.
  

  同一优先级的运算符，运算次序由结合方向所决定。

  简单记就是：！ > 算术运算符 > 关系运算符 > && > || > 赋值运算符

  C Operator Precedence Table

  This page lists C operators in order of precedence (highest to lowest). Their associativity indicates in what order operators of equal precedence in an expression are applied.

  Operator	Description	Associativity
  ( ) [ ] . -> ++ --	Parentheses (function call) (see Note 1) Brackets (array subscript) Member selection via object name Member selection via pointer Postfix increment/decrement (see Note 2)	left-to-right
  ++ -- + - ! ~ (type) * & sizeof	Prefix increment/decrement Unary plus/minus Logical negation/bitwise complement Cast (convert value to temporary value of type) Dereference Address (of operand) Determine size in bytes on this implementation	right-to-left
  *  /  %	Multiplication/division/modulus	left-to-right
  +  -	Addition/subtraction	left-to-right
  <<  >>	Bitwise shift left, Bitwise shift right	left-to-right
  <  <= >  >=	Relational less than/less than or equal to Relational greater than/greater than or equal to	left-to-right
  ==  !=	Relational is equal to/is not equal to	left-to-right
  &	Bitwise AND	left-to-right
  ^	Bitwise exclusive OR	left-to-right
  |	Bitwise inclusive OR	left-to-right
  &&	Logical AND	left-to-right
  | |	Logical OR	left-to-right
  ? :	Ternary conditional	right-to-left
  = +=  -= *=  /= %=  &= ^=  |= <<=  >>=	Assignment Addition/subtraction assignment Multiplication/division assignment Modulus/bitwise AND assignment Bitwise exclusive/inclusive OR assignment Bitwise shift left/right assignment	right-to-left
  ,	Comma (separate expressions)	left-to-right
  Note 1: Parentheses are also used to group sub-expressions to force a different precedence; such parenthetical expressions can be nested and are evaluated from inner to outer. Note 2: Postfix increment/decrement have high precedence, but the actual increment or decrement of the operand is delayed (to be accomplished sometime before the statement completes execution). So in the statement y = x * z++; the current value of z is used to evaluate the expression (i.e., z++ evaluates to z) and z only incremented after all else is done. See postinc.c for another example.