how to get all files on a directory of .c file

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http://www.unix.com – i need to get all files names on a c file directory to I can open every file and read from them to write on other files...... I solved the problem of reading and writing for a specific file to another file .... but i want that for text files in .c file directory so how to read a names of files 1 by 1 I searched a lot but no codes about that (HowTos)