Checking if value is in range fails with "Operator `<=' cannot be applied to operands of type `bool' and `int'"

Question

Trying to check if an integer value falls into a range however it is giving me a compile time error

Operator '<=' cannot be applied to operands of type 'bool' and 'int'

int n = 3; // read from user like Convert.ToInt32(Console.ReadLine().Trim());
    
if ( 2 <= N <= 5)
{
    Console.WriteLine("In range");
}

What is the correct way to check if a value falls into a range and why the way I wrote the check causes this error?

in c#, you cannot write stuff like `2<=N<=5`. you have to separate the checks: `2<=N && N<=5`. i recommend [the manual](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/) as reference — Franz Gleichmann, Sep 29 '21 at 18:25

score 3 · Answer 1 · answered Sep 29 '21 at 18:25

You can't do this:

(2<=N<=5)

You have to do it as two:

(2<=N && N<=5)

(Trying to do it as one means c# will resolve the 2<=N to some boolean, e.g true and then try to do true<=5 - this gives rise to the error that "<= cannot be used to compare a boolean to an integer")

Joel Coehoorn · Answer 2 · 2021-09-29T18:42:04.527

This doesn't work they way you think it does:

(2<=N<=5)

What really happens here is the compiler first evaluates the 2<=N part of the expression as producing a boolean result. It then wants to use this boolean result for the <=5 part of the expression... and that's not allowed. C# does not let you implicitly compare a boolean with an integer, and even if it did it's doubtful the result would match your intention for the code.

Instead, you need to do this:

if( (2 <= N && N <= 5) || N > 20 )

The same applies to the 6<=N<=20 expression.

Finally, I might reduce the logic to eliminate nesting and repeated outcomes, like this:

int N = Convert.ToInt32(Console.ReadLine().Trim());

if(N % 2 !=0 || (6 <= N && N <= 20 ))  
{
    Console.WriteLine("Not Weird");
}
else if( (2 <= N && N <= 4) || N >20 ) //4 rather than 5, because we know N is even
{
    Console.WriteLine("Weird");
}
else // N is even and <=0
{
    Console.WriteLine();
}

Checking if value is in range fails with "Operator `<=' cannot be applied to operands of type `bool' and `int'"

2 Answers2