i write alot of program in C. and it really helpful if i write them in unix or linux. so is there a way for me to use unix or linux without downloading onto my computer? may be i can download unix, linux on CD or some program that let me do this.
Why not install VMware or another virtual app on your host computer, then install Linux, etc as virtual guest operating systems so you don't disrupt your host computer's OS. When you are do e with the guest, you simply delete the VM files.
To run a virtual host on your machine, you need the software.
Start by downloading 'Virtual Box'. It's free software and works very well. I use it every day.
In VirtBox, you can create a new virtual machine using the wizard. Setup the memory, hard drive size, etc. You'll need to download a Linux ISO from whatever distro you want to try. In the VirtBox CDRom for that new virtual host, mount the ISO. Then start the virtual host. It would boot from CD and start loading the ISO just like a normal machine.