The swapbuffers function is available in the winbgim implementation of BGI graphics. You do not need to include conio.h; just include graphics.h. The function swaps the roles of the current active and the current visual graphics buffers. It is equivalent to these statements:
int oldv = getvisualpage( );
int olda = getactivepage( );
setvisualpage(olda);
setactivepage(oldv);