CODEWITHSUNDEEP
c#if-statementnumbersoperatorsrelational
Gintas_
Gintas_

Reputation: 5030

Why does this number gets detected as bool?

I'm checking if value ir between 0 and -0.2 like so:

float value = -0.1;
if (0 < value > -0.2f) { }

But I get error operator '>' cannot be applied to operands of type 'bool' and 'float'. I know, I could to that in other way using && operator in that if sentence, but I want to know, why does it gets detected as bool?

Upvotes: 0

Views: 141

Answers (5)

Dave Lawrence
Dave Lawrence

Reputation: 3929

float value = -0.1;
if (0 < value > -0.2f) { }

Because you need to seperate the comparisons

Most langauges work left to right so 

0 < value

will be evaluated first. The result of this a boolean

Now your expression reads as

boolean > -0.2f

Which obviously will not work. You need

if (0 < value && value > -0.2f)

&& is a 'logical and' which combines the results of the logical computation to the left and right of it

Upvotes: 4

bsa
bsa

Reputation: 2801

Your if statement is syntactically incorrect. It requires a boolean expression between the braces.

http://msdn.microsoft.com/en-us/library/vstudio/5011f09h.aspx

if (0 < value > -0.2f) { }

Your statement is parsed like this:

if ((0 < value) > -0.2f) { }

(0 < value) evaluates to boolean expression. You're attempting to compare this to a float. Hence the error.

As you suggested yourself, the normal way to do this is to use &&.

Upvotes: 0

It&#39;sNotALie.
It&#39;sNotALie.

Reputation: 22794

Because of order of operations.

Basically, the compiler compile the if to something like this:

if ((0 < value) > -0.2f)

And the result of that is comparing a bool and an int, which is not good.

Try this instead: 

if (0 < value && value > 0.2f)

Upvotes: 0

Zbigniew
Zbigniew

Reputation: 27594

Take a look at this:

0 < value > -0.2f

Firstly 0 < value is evaluated, it returns bool value then it tries it compare bool to float number -0.2f, so it returns error, because it is not permitted.

You want to check if value is less and if value is greater than, so this is what you want to do:

if (0 < value && value > -0.2f) { }

Upvotes: 7

Esoteric Screen Name
Esoteric Screen Name

Reputation: 6112

It's because of the construction of your if statement. Try this instead:

if (0 < value && value > -0.2f) { }

What you've written is equivalent to this:

if ((0 < value) > -0.2f) { }

The 0 < value comparison is being evaluated, returning a boolean, which then becomes the operand for the second comparison. And, as the error message says, you can't use > to compare a boolean and a float.

Upvotes: 1

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