Bug? Variable defined as Long acts link Int

[Gary Milne]

This code:

Dim Diff1 As Long = (999999 * 1000)
Log ("Diff1 is:" & Diff1)

Dim Diff2 As Long = (999999 * 2000)
Log ("Diff2 is:" & Diff2)

Dim Diff3 As Long = (999999 * 3000)
Log ("Diff3 is:" & Diff3)

Dim Diff4 As Long = 2147483647 + 1
Log ("Diff4 is:" & Diff4)

Generates this output.
Diff1 is:999999000
Diff2 is:1999998000
Diff3 is:-1294970296
Diff4 is:-2147483648

 

[Roycefer]

This is expected and normal behavior. In all 4 cases, you're doing operations on two Ints and then assigning the resulting value to a Long. Consequently, the Int overflow will occur before a Long is created and any values are stored in it.

Instead, try this:

Dim Diff3 As Long = 999999
Diff3 = Diff3 * 3000
Log("Diff3: " & Diff3)

This makes sure that 999999 is stored in a Long and that the resulting 999999*3000 is performed as Long multiplication and not Int multiplication.

 

[Gary Milne]

Thank you, that does explain it in that the right hand side is evaluated first. I think making the temporary value that holds the Int * Int of the same type as the left hand side would be more intuitive. Don't mind the rules though as long as I know what they are.