What does "If a < b < c Then" actually do in vb.net?

Question

Here is some "bad" code:

Module test
    Sub Main()
        Console.WriteLine("1<2 =   " + cstr((1<2)))
        Console.WriteLine("2<1 =   " + cstr((2<1)))
        Console.WriteLine("1<2<3 = " + cstr((1<2<3)))
        Console.WriteLine("3<2<1 = " + cstr((3<2<1)))
    End Sub
End Module

The output from this is:

1<2 =   True
2<1 =   False
1<2<3 = True
3<2<1 = True

1<2<3 is True, but not for the right reasons.

3<2<1 evaluates to True as well. Why?

Can someone explain what's going on here?

I know I should be using a<b and b<c but I want to know what happens when you use consecutive operators. ie, why doesn't the compiler cry!! Is syntax like this used for something else?

Answer 1

It evaluates it left to right, so 3<2<1 is the same as (3<2)<1. Because expression in parentheses is false, the whole thing evaluates to 0<1 which is true.

Answer 2

First of all, with Option Strict On, the compiler does cry. With Option Strict Off, here's what happens:

• 3 < 2 < 1 is evaluated from left to right, so it's the equivalent to (3 < 2) < 1
• 3 < 2 is evaluated to False so the compiler evaluates: False < 1
• VB converts boolean value False to 0, so that it can be compared with another int value
• 0 < 1 is evaluated to True