1) if your files will be in program execution folder, there is no need to specify full path.
2) strcat("D:/TUGAS/1/1",b); You cannot do that. It will try to append b string to const literal, what is forbidden but will work because of compatibility conversion to char* (Should give you a warning).
3) Even it it would work, you forgot another slash at the end of line, so if you enter "test", you wil be trying to open "D:/TUGAS/1/1test"
here's something about windows:
1)- windows -unlike linux- uses a backslash, not a slash.
2)- and in c++, you can't write a backslash directly, to write a backslash in a string literal you should write two backslashes.
replace line 6 with this:
what the use of "R", if i add it, the program error
Oh, you have an outdated compiler which doesn't support C++11.
Ok, use "D:\\TUGAS\\1\\1\\"
I want to see, what exactly you are typing, and screenshot of folder with actual files.
I am typing "Velocities.xls"
My folder looks like http://gm4.in/i/du0.png