Spot the Bug

One of our students is having problems with his C# conditions:

if (HighestSales <= EachSales );
    Console.WriteLine ("new top score");

It always prints the message. Why?

Comments

[Alcides Fonseca]

There's an extra ; after the end of the if condition. That means it will take no action, and whatever comes next is always executed. If you remove it, it will work.

A lot of programmers always use the curly braces since it's probable that you will add stuff there in the future. For example:

if (HighestSales <= EachSales) {
Console.WriteLine("new top score");
HighestSales = EachSales;
}

[Alfred Thompson]

Prime example of one of the reasons I am not a fan of the semi-colon curley brace school of programming languages. :-)

[PhilC]

In perl you can do cute things like:

print('New Top Score') if (HighestSales <= EachSales);

Which I like a lot :-), and it only uses one ';'.

I like curly brackets too! :-P

[JDog - Joel Parkey]

Not to mention it should be referenced in accordance to the EachSales compared to the Highest sales, and the colon messes things up aswell.

i'd do...

if(EachSales >= HighestSales)
{
EachSales = HighesSales;
Console.WriteLine("New Highest Sales: " + HighestSales);
}

sorry, formatting messed me up. I also think DeMorgans theroem might be involved somehow, or am I trying to cover too many bases?

:)

[Shawn]

The extra semi-colon, agreed.

I would question though, even though single lines after the condition are valid C# (I always use curly brackets myself), does the ; just act like an empty { } even though they are not used? Just curious.

[JDog - Joel Parkey]

@Shawn

I can't post comments on my own blog :( but I did read yours and would be interested, especially since Silverlight seems viable we should stick to a unifying language of C#.

[[ICR]]

I do think it's a little silly they carried this practice over to C#. If you want an empty control block you could just do { } and then removing the ability for ; to be an empty control block would stop this common beginner error.

[Rob]

Well done everyone. Visual Studio gives you a wavy "are you sure you want to do this" blue line underneath the offending character, but I agree that it is confusing.

On the other hand, I really want my students to understand that in programming the effect of a single misplaced character can be enormous, and that the machine never knows enough to "understand" what you are trying to do. So the only way forward is to get it right....

[JDog - Joel Parkey]

To be specific that above code wouldn't print anything, would it Rob ? As it happenned in our quiz you posted on ebridge today there was a trick question much like this. Is 16/20 considered Ok ?

[Rob]

The code would always print "New Top Score". And 16/20 is a very good mark.

[JDog - Joel Parkey]

It would but I was referencing the question,

if(1 >= 0){
Console.WriteLine("X");
}

X would be printed wouldn't it ? or did you mean that statement, with no main initialised and such.

Anyhoo, its over now and you must be jetlagged so i'll let you have a break.