If statement logic reverse

Question

bool x = someFuncThatReturnsTrueorFalse();
if (!x && (str1.length() != str2.length()) {
    // do nothing
} else {
    // do something
}

How would I rearrange the code above to eliminate the else statement? I need to do nothing if bool = false and str1 and str2 have different lengths. Otherwise, I need to do something (e.g. function call).

For the life of me, I can't think of any way to change this. Let me know if you need further details.

Trivial boolean algebra. The opposite of `if (A && B)` is `if (!(A && B))` which is equivalent to `if ((!A) || (!B))`. — Peter, Sep 22 '20 at 00:58

MikeCAT · Answer 1 · 2020-09-22T00:59:18.597

1

The simplest way is putting !() around the condition.

bool x = someFuncThatReturnsTrueorFalse();
if (!(!x && (str1.length() != str2.length())) {
    // do something
}

Another way is using De Morgan's laws: !(A && B) is equivalent to !A || !B.

bool x = someFuncThatReturnsTrueorFalse();
if (x || (str1.length() == str2.length()) {
    // do something
}

edited Sep 22 '20 at 00:59

answered Sep 22 '20 at 00:39

MikeCAT

73,922
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`bool` is a keyword. – cigien Sep 22 '20 at 00:40
@cigien It may be defined as macro. – MikeCAT Sep 22 '20 at 00:41
@cigien [C++ preprocessor #define-ing a keyword. Is it standards conforming? - Stack Overflow](https://stackoverflow.com/questions/2726204/c-preprocessor-define-ing-a-keyword-is-it-standards-conforming) – MikeCAT Sep 22 '20 at 00:43
This is the right [answer](https://stackoverflow.com/a/52203750/8372853), as the comment points out :) Maybe not UB, but definitely not allowed. – cigien Sep 22 '20 at 00:44
Sorry for the confusion, this was meant to be pseudo-code. I have just updated to avoid any further confusion. – user3354230 Sep 22 '20 at 00:57
@user3354230 Thank you for notifying. Updated answer according to that. – MikeCAT Sep 22 '20 at 00:59

score 0 · Answer 2 · answered Sep 22 '20 at 07:41

0

There is nothing wrong leaving as is. The code will still compile

answered Sep 22 '20 at 07:41

Angus

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If statement logic reverse

2 Answers2