Can you spot the problem?

by Miha Markič 28. June 2007 14:16

Check out this code:

static void Main(string[] args)
{
    string test = null;

    Console.WriteLine("Is test null: " + test == null);
    Console.ReadLine();
}

And guess the output without running the code.

Tags:

.net

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Comments (4) -

Josh
Josh
6/28/2007 7:14:20 PM #

Can you explain that outcome. I guess wrongly true. Interested in hearing your feedback.

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Giuseppe
Giuseppe
6/28/2007 7:37:20 PM #

i guess "false"
because the first step is to concat "is test null:" + test --> "is test null:
and after the concatination the string will be compared to null --> false

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Miha Markic
Miha Markic
6/28/2007 8:40:01 PM #

Hi Josh,

Giuseppe is correct. The order of operators is misleading in this case. As a human you know what you want to achieve and it seems logical that it will work, but the operator precedence is not what you would think. Smile + has a precedence over ==.
One can find the operator precedence order here:
msdn2.microsoft.com/.../6a71f45d(VS.80).aspx

Reply

Giuseppe
Giuseppe
6/29/2007 7:04:51 PM #

i have a good riddle as well (T-SQL):
SELECT DATEADD(MONTH, 1 , '20070131')

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Miha Markic

About me
Righthand
 
Microsoft MVP
 
Developer Express' DXSquad
INETA Country Leader for Slovenia
INETA Country Leader for Slovenia
Slovene Developer Users Group Lead
Friends of Red-Gate
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Miha currently works as a free lance consultant and software developer specialized in .net area.
He graduated in Computer and information science at the University of Ljubljana, Slovenia. He has accumulated experience in various programming languages such as Java, Visual Basic 3-6 (MCP), Visual C++, Delphi, C# and VB.Net through years.
He has experience in practically all (technical) stages of project development, including planning, framework development, user interface, business processes, as well as testing and documenting. He has worked on big and small projects in Slovenia and abroad (e.g. participated in completing level 3 IS for the Nucor steel plant, Hertford, USA).
Currently he enjoys programming in .net environment using C#. Since 2000 he has been active in Developer Express' DX Squad and has been ECDL trainer and tester. He also gives lectures on conferences and other events in Slovenia.

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