Boolean Operators..&& (AND) is working but ! (NOT) is'nt working

Using Arduino Programming Questions
1

Hi there,
I'm trying to use NOT but unfortunately even with the codes below, arduino never gets into the second if.

 if((readString.indexOf("test") >0) && (readString.indexOf("test2") >0))
 { 
   //1   
 }//checks for test words

  if((!readString.indexOf("test") >0) && (!readString.indexOf("test2") >0)) 
{  
   //2   
  }  //check if there aren't any test words

No1 is working like a charm but No2 isn't for some reason.
When I check for 1, I type "test" and "test2", but when I check for 2 I type other words. It never gets into 2.
Can anyone explain to me why this is happening?

2

You are applying the not to the wrong thing. What you want it !(readString.indexOf("test") >0).

Although, I think that is atrocious code. It's much better to change the value that readString.indexOf() is being compared to, in my opinion.

3

nathanas:

  if((!readString.indexOf("test") >0) && (!readString.indexOf("test2") >0))

See the operator precedence: C++ Operator Precedence - cppreference.com

Note that ! is a higher precedence than >.

Consider what happens when we parenthesize by precedence:

if( !(readString.indexOf("test")) >0 && !(readString.indexOf("test2")) >0 )

PaulS is right too:

readString.indexOf("test")) <= 0

is a much more readable test and faster to type.

4

Thanks for sharing guys!
Made it working. :slight_smile: