c中的逻辑AND和OR

Question

In a && b , this returns true if both a and b are equal to 1. If a=-1 and b=-1 then also the expression returns true.Similar is the case with a||b,where a=-1 and b=0,it returns true. Can anybody please explain the reason.

Answer 1

a && b returns 1 when both a and b are nonzero , not just when they're equal to 1. Otherwise it returns 0.

a || b a || b returns 1 when at least one of a or b is nonzero , not just when one of them is equal to 1. Otherwise it returns 0.

To give some examples:

   0 &&  0 -> 0
   1 &&  0 -> 0
   1 &&  1 -> 1
   2 &&  1 -> 1
  -1 && -1 -> 1
-100 &&  0 -> 0

   0 ||  0 -> 0
   1 ||  0 -> 1
   0 ||  1 -> 1
  -1 ||  0 -> 1
-100 || 20 -> 1

Answer 2

C11 (n1570) §6.5.13 al 3 p 99 say :

The && operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it yields 0.

-1 is a nonzero value, so -1 && -1 is 1 .

Answer 3

On the MSDN page for && :

The logical-AND operator produces the value 1 if both operands have nonzero values.

Clearly both operands are -1 in your example so they will produce 1.

On the same page, listed for ||

If either operand has a nonzero value, the result is 1.

In your case one operand is -1, therefore the result is 1

Answer 4

AND returns 1 if both operands have non-zero values. OR returns 1 if either operand has a non-zero value.

Answer 5

运算符ie（&&）只有在两个条件都为真的情况下才会继续运行，如果是运算符，则运算符即（||）如果两个条件中的至少一个为真，则继续运行。

Answer 6

逻辑运算符返回0或1.如果&&运算符的两个操作数都不是0.Else，它返回0.返回0.语句如if（x），while（x）等。如果参数不是0，则执行。对于所有其他+ ve和-ve参数，它将被执行。