1. open the input file, checking for file-open error
2. open the output files, checking for file-open errors
3. for each line in the input file
4. use a regex or split to see if it has the date you want
5. write it to the appropriate output when appropriate
6. close the files

Please try to do that yourself and if you have problems, feel free to come back and tell us which steps are giving you problems.