Comparing values in 2 textfiles and returning the missing values

From: Jorgen Gustafsson (jorgen.xi.gustafsson_at_ericsson.com)
Date: 12/11/03 

Date: Thu, 11 Dec 2003 16:58:04 +0100

Hi,
im trying to write a small progam to compare data in 2 textfiles.

I want to search for values that doesnt exist in File2.
The result should be "3" in the example below but Im not
able to do this since my program crosschecks all numbers in
both files and Im getting a lot of "hits". (outer and inner while-loops)

 
Below is an examples of the textfiles:

File1.txt File2.txt
1 1
2 2
3 4
4 5
5 6
                7
                8
                9
                10

Thanks in advance...!
Jorgen