GCC compiler errors with "No such file or directory"

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http://askubuntu.com – My Ubuntu version is 12.04 LTS. I have written some C programs. But there is a compiler-problem. I've googled and found that I need build-essential. So I download and installed it. After installation, it worked well. But after maybe 3 hours, the problem happened again. When I write: gcc -o -std=c99 sort sort.c The compiler complains: gcc: error: sort: No such file or directory. I have no idea now. (HowTos)