CODEWITHSUNDEEP
c#
mrblah
mrblah

Reputation: 103477

What will this method return, true or false?

bool isValid = false;
string username = "someadmin";

If( !String.IsNullOrEmpty(username) && !( username.IndexOf("admin") != -1)
    isValid = true;

The second part with the double negatives is crossing me up!

Upvotes: 0

Views: 926

Answers (8)

Kenneth Reitz
Kenneth Reitz

Reputation: 8846

The value stored in isValid will be false.

Upvotes: 0

i_am_jorf
i_am_jorf

Reputation: 54600

May I present to you DeMorgan's Laws:

NOT (P OR Q) = (NOT P) AND (NOT Q)
NOT (P AND Q) = (NOT P) OR (NOT Q)

So, you could rewrite it as:

if (!(String.IsNullOrEmpty(username) || username.IndexOf("admin") != -1)) {
    isValid = true;
}

...thus removing the double negatives.

Furthermore, you could say:

if (String.IsNullOrEmpty(username) || username.IndexOf("admin") != -1) {
    isValid = false;
}

...which removes all the negatives.

Also, you could say:

isValid = !(String.IsNullOrEmpty(username) || username.IndexOf("admin") != -1));

...to make it nice and compact.

Upvotes: 10

Decent Dabbler
Decent Dabbler

Reputation: 22773

It will give you a syntax error due to a missing paren ;-)

But seriously, it will return false.

!String.IsNullOrEmpty(username) // if username is NOT null and NOT empty => true

username.IndexOf("admin") != -1 // if "admin" IS FOUND in username (not -1) => true

!( username.IndexOf("admin") != -1 ) // if "admin" IS NOT FOUND in username => false

So, concluding: the conditions of the if statement are NOT met, so isValid will remain false.

PS.: I'm not a c# programmer, but I presume that when IndexOf(string) equals -1, it means not found.

Upvotes: 0

olle
olle

Reputation: 4595

false. But I don't get the question? Couldn't you just execute this? What double negatives? The value is just being inverted and the parentheses clearly indicate the order in which the statements are executed.

Upvotes: 0

Jon Onstott
Jon Onstott

Reputation: 13727

A plain language version:

if (username is not null or empty and username doesn't contain "admin") isValid = true;

Upvotes: 1

LukeH
LukeH

Reputation: 269278

isValid will be false.

(Nitpick: this code doesn't "return" anything: it just sets the value of the isValid variable.)

Upvotes: 0

Stephanvs
Stephanvs

Reputation: 731

It'll return false.

Upvotes: 1

Ropstah
Ropstah

Reputation: 17784

it will return false

!String.IsNullOrEmpty(username)          // this is true, the string is not NullOrEmpty
!(username.IndexOf("admin") != -1)       // IndexOf is >= 0, so != 1 is true. But the first ! makes it false

So IsValid will contain the same value as it had at the beginning...

Upvotes: 4

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