C++: Why does this logical expression evaluate to false?

Question

int a = 10, b = 12, c = 8

!((a < 5) || (c < (a + b)))

I just tried it in a compiler and it was false.

Break it down step by step and tell us what you think each step should result in. — chris, Jun 10 '14 at 02:46

score 3 · Accepted Answer · answered Jun 10 '14 at 02:51

The inner expression:

(a < 5) || (c < (a + b))

evaluates a < 5 as false (since a is 10) and c < (a + b) as true (since 8 is less than 10+12). Performing a Boolean "or" operation on false and true gives you true.

And, given that the next thing you do to that value is the ! (inversion), that true turns into a false.

score 0 · Answer 2 · answered Jun 10 '14 at 02:48

0

c < (a + b) == 8 < (10 + 12) == 8 < 22 == true
a < 5 == 10 < 5 == false
(a < 5) || (c < (a + b)) == false || true == true
!((a < 5) || (c < (a + b))) == !(true) == false

answered Jun 10 '14 at 02:48

S. Ahn

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C++: Why does this logical expression evaluate to false?

2 Answers2