i am using Ubuntu 8.04

What is GCC?
How do i know if my Linux has GCC?
How do i check my GCC version?

thank you

Congratulations!
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GCC=GNU Compiler Collection. It is used to compile C/C++ and other programs.

You installed it. You normally know if you have installed something. Of course, you can also find out by trying to invoke it in a terminal, thus:

~$ gcc
gcc: no input files

... so, gcc is installed. If it had said - bash: gcc: command not found - then gcc is not installed.

Ubuntu 8.04 does not have development tools by default. You install the main set with:

sudo apt-get install build-essential

$ gcc --version
gcc (GCC) 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2)
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

... so my version is 4.1.3

I take it you have tried to install something and got an error that it needs gcc version xyz?

That will only show if the manpage is installed. It has been known for these to be installed without the program.