Thread: boolean

Computers in general see things are either true or false. Everything is.

The common logical operators are:
OR - if one OR the other is true.
AND - if BOTH are true.
NOT - it's true when it's NOT true.

In computers, we use this to solve problems where something has to be combined with something else:

Code:

if (input > 0 && input < 5) 
   ... do something  
else
   ... out of range

The if-statement is true when input is greater than 0 AND inptu is less than 5 (so the valid range is 1..4 if input is an integer).
or

Code:

if (a == 7 || (b == 8 && c == 9))
{
   ... do some stuff
}

True if either a is 7, or if both (b is 8 and c is 9). It will also (see below) be true if a is 7 and b is 9 and c is 9 - since EITHER side can be true to give a true result.

Note that OR in computers is "inclusive", not like humans where we see OR mostly as an exclusve combination: Are you married or single, do you want coffee or tea. Those can not be true at the same time (unless you are lying or like strange hot drinks).

There is a logical operator called "XOR" which is "exclusive or" - it is only available as a binary operator in C and C++ (using the ^ symbol). It is truly a OR in human ways: If one side is true and the other is false, the result is true. But we don't use that in C or C++ boolean logic.

Computer AND is much more like our "human AND" - both sides need to be true for the result to be true.

--
Mats