kiranmayi Talusani

Divya,
I think your program is only comparing first line from the first file with all the lines from the second file,because the value of 'str' becomes 'null'.
when the program's execution comes out of the second(inner) while loop the value of 'str' will become 'null'. Then it will read second line from frist file.But it will not enter into the second(inner) while loop because the value in str is 'null'. so it will read all the lines from first file util the value in 'line' becomes 'null' and then it comes out of the first(outer) while loop.

divya,
First your program is comparing first line from first file with all the lines from second file.

After that it is comparing all the lines from the first file with the last line(after first line is compared with all the lines from second file, the value in "str" will be last line from second file) from second file.I guess that is the reason you are not seeing the currect output.