Is there a simple lite-c code explaining how to make a file requester for a user to select files for loading or saving.

look at file_dialog...

Unfortunetly it does not work in full screen mode, only in window mode. Any solutions?

Use a panel or TEXT, this also works in fullscreen mode. There is a function, I've forgotten the name, that reads the directory content into a TEXT. You can make a file requester with it.

The function is called txt_for_dir.

I solved the file_dialog problem this way and it now works great.

#include <strio.c>

function loadgame()
{
wait(1);
video_switch(0,0,2);
char* filename = file_dialog("Load Saved Game","*.ssv");
video_switch(0,0,1);
var filehandle = file_open_read(filename);
...
}