Decimal to binary error

[CoderVB]

I've been trying to fix this code for a school project but still can't. Please help I'm newbie. Need to convert max of 10 decimal numbers to binary but this code only limited to 4 dec digits.

Dim number as integer
Dim binary_string as string

Number = val (text1.text)
Binary_string = " "
Do while number > 0
    Binary_string = number mod 2  & binary_string
    Number = number / 2
Loop
Text2.text = binary_ string

End sub