&&, ||, ! in C++?

What does ! mean in C++?





Also, can you use %26amp;%26amp; and || in the following context





If (x == 0 %26amp;%26amp; y == 0)


{


cout %26lt;%26lt; "blah blah";


}





or the same thing but replacing %26amp;%26amp; with ||?

%26amp;%26amp;, ||, ! in C++?
! means logical not.


%26amp;%26amp; means logical and.


|| means logical or.





If you need further explanation of these, look at truth tables.





The following code is correct.


It will evaluate x. If x equals 0, then it will evaluate y. If y also equals 0 then it will output blah blah, otherwise it will not.


If (x == 0 %26amp;%26amp; y == 0)


{


cout %26lt;%26lt; "blah blah";


}





If you were to replace the %26amp;%26amp; with ||, then it would evaluate x. If x equals 0, then it will output blah blah. Then it will evaluate y. If y equals 0, then it will output blah blah, otherwise it will not.


If (x == 0 || y == 0)


{


cout %26lt;%26lt; "blah blah";


}





To use the ! symbol, this will only output blah blah if the expression evaluates to false, that is both x and y equal 0.


If (!(x == 0 || y == 0))


{


cout %26lt;%26lt; "blah blah";


}
Reply:Ya lerry is right ! is logical not.





see suppose if u have 2 values for x and y say





1. x=0;y=0;


2. x=0;y=1;


3. x=1;y=0;


4. x=1;y=1;





for statement





If (x == 0 %26amp;%26amp; y == 0)


{


cout %26lt;%26lt; "blah blah";


}


if input is 1 i.e. x=0, y=0





output blah blah





else for all other inputs i.e. 2,3,4, ands if statement will not execute.





similarly


for statement


If (x == 0 || y == 0)


{


cout %26lt;%26lt; "blah blah";


}





for input 1,2 and 3 it will print blah blah





and for input 4 it will not execute if loop.
Reply:That's the primary use for %26amp;%26amp; -- to join two logical expressions into a single one.





! is the negation operator: ! (False) == True





But %26amp;%26amp; and || are NOT interchangeable. %26amp;%26amp; means AND, while || mean OR. In fact, there's a theorem in logic named after the mathematician DeMorgan that relates %26amp;%26amp; and || this way:





!(A %26amp;%26amp; B) == ( !A || !B )


and


!(A || B) == ( !A %26amp;%26amp; !B )





So while the %26amp;%26amp; can be used in either context you mention,


(x == 0 %26amp;%26amp; y == 0) does not equal ( x == 0 || y == 0 )





Hope that helps.