hello, does anyone know how to creat a new .dat file by using C?

To open a new file, use

FILE fp;

fp = fopen("filename", "w");
if (fp == NULL) {
/* the open failed */
exit();
}

The "w" says to open the file in "write" mode, which causes it to make a new file, even overwriting the file if it already exists.

If you want a .dat file, just set the filename to include a .dat ("filename.dat")

The normal way to write the above code is:

if ((fp = fopen("filename","w")) == NULL) {
fprintf("Failed to open the file\n");
exit();
}

You'd have to include stdio.h (for the fopen() and fprintf() and stdlib.h (for the exit())