这是对逻辑“和”运算符的正确使用吗？

Question

I'm looking at someone's code and they did:

if ( myNum > (num1 && num2 && num3) )

... with the intent of executing code when myNum is greater than num1, num2, and num3. Will this work?

edit: Thanks guys. I didn't think it would work, but I'm no expert, so I thought I'd ask people who are.

Answer 1

Assuming the values are of a type like int , in C or C++ this would first evaluate

(num1 && num2 && num3)

as

(num1 !=0) && (num2 != 0) && (num3 != 0)

The result would be either true or false in C++, and either 1 or 0 in C.

You would then compare myNum to that result.

Answer 2

No - certainly not in C# or Java, at least. You want:

if ((myName > num1) && (myNum > num2) && (myNum > num3))

(It's possible that you don't need the brackets here - I can never remember operator precedence.)

It wouldn't work as written in Java or C# as && is an operator on Boolean operands, with a Boolean result. It's possible that it would compile/run in a less strongly-typed language, but I highly doubt that it will have the intended effect in any mainstream language.

Answer 3

No, that won't work. Why it won't work depends on the language, but (num1 && num2 && num3) will be evaluated first in all the languages you've tagged the question with. Provided (num1 && num2 && num3) actually compiles and evaluates to something, you will then get myNum > something.

Answer 4

Not in any language from the tags. Well, I think it might work in C and JavaScript, but certainly not as intended.

Answer 5

It might work in c++ if myNum, num1, num2 and num3 are a special type with operators > and && overloaded. But it will probably not worth it creating such a class which can handle this.

Answer 6

This is incorrect at least in C: http://codepad.org/R9IP0ZOr

int main()
{

  int myNum = 10;
  int num1,num2,num3 ;
  num1 = 15;
  num2 = 16;
  num3 = 17;
  if ( myNum > (num1 && num2 && num3) )
      printf("%s","YES|GREATER");
  else
    printf("%s","NO|SMALLER");
}   // prints "YES|GREATER"  even though all numbers are greater than myNum

Correct statement should be :

if(  (myName > num1) && (myNum > num2) && (myNum > num3) )
{
}

Answer 7

It is valid JavaScript code, but will probably work differently than expected by the person who wrote it.

It will actually end up evaluating if(myNum > num3) since (num1 && num2 && num3) will just return the value of num3

Answer 8

或更幻想：

if(Num > Math.Max(Num1,Math.Max(Num2,Num3)))