Using Boolean operators

Question

This works fine

if ((a >= 40 && a <= 50) || (a >= 60 && a <= 80))
// do something

How do I do the reverse of it?

if ((a < 40 && a > 50) || (a < 60 && a > 80))
// do something

The code does not work as expected. I want something like if not (condition)

Answer 1

You might want to look at De Morgan's laws.

1. !((a >= 40 && a <= 50) || (a >= 60 && a <= 80))

2. (!(a >= 40 && a <= 50) && !(a >= 60 && a <= 80))

3. ((!(a >= 40) || !(a <= 50)) && (!(a >= 60) || !(a <= 80))

4. ((a < 40 || a > 50) && (a < 60 || a > 80))


or in other words: (a < 40 || (50 < a && a < 60) || 80 < a)

Answer 2

if ((a < 40 || a > 50) && (a < 60 || a > 80))
// do something

Answer 3

While I would recommend figuring out how to make it work properly (by rewriting it)

if (!((a >= 40 && a <= 50) || (a >= 60 && a <= 80)))

should work I believe.

Answer 4

You need a "OR"

if ((a < 40 || a > 50) && (a < 60 || a > 80))

Or, a NOT

if (!((a >= 40 && a <= 50) || (a >= 60 && a <= 80)))

Answer 5

You second example

if ((a < 40 && a > 50) || (a < 60 && a > 80))

doesn't make sense as a cannot be both less than 40 and greater than 50 (or less than 60 and greater than 80) at the same time.

Something like

if (!((a < 40 && a > 50) || (a < 60 && a > 80)))

or

if ((a < 40 || a > 50) && (a < 60 || a > 80))

Answer 6

if (!((a >= 40 && a <= 50) || (a >= 60 && a <= 80)))

Answer 7

Assuming that you want the equivalent of

if ( not ((a >= 40 && a <= 50) || (a >= 60 && a <= 80)) )

then, if you think about the original expression, it should be

if (a < 40 || (a > 50 && a < 60) || a > 80)

The first expression is allowing a to be a number from 40 to 50 or from 60 to 80. Negate that in English and you want a number less than 40 or between 50 and 60 or greater than 80.

De Morgan's Laws can get you an accurate answer, but I prefer code that you can read aloud and make sense of.