How do I handle this error with ifstream and ofstream??

[kangdh2140]

I make a simple program with file I/O.
So I use ifstream and ofstream.
So I coded
std::ifstream file_in("input.txt");
std:fstream file_out("output.txt");
(input.txt and output.txt is at same dir that contains my program)
.
But when my program run, it can`t open that files.

HOW DO I HANDLE THIS ERROR???