The output seems to be the same... I don't understand where the mistake was made.

http://www.learntosolveit.com/cprogramming/Ex_5.11_conddetab.html First mistake is, you use a copy sourcecode. without any fix. That code can only useful when tab_num is exactly 8. This problem is say, "문제의 첫번째 줄에 1개의 탭에 대해 몇개의 공백으로 치환되는지 명시됩니다." . The number which locate in first line mean "Tab Size". For example if first line number is 5. ab'\t'cd become ab cd (three space). not ab cd(two space) because tap size is 5. so you must start the next character start with 5th coloumn your co....no. THAT sourcecode is not consider about tabsize input. fix this

I have fixed that issue, but I am still getting Presentation Error.

Hmm... algorithm seems work well... I think MAX LINE is too short, maybe?