Use: EnumDisplayMonitors(NULL,NULL,MonitorGetSize,0);

with callback function:
void MonitorGetSize(long hMonitor, long hdcMonitor, RECT* MonitorRect, long dwData){
static int i = 0;
sizex[i] = MonitorRect.right - MonitorRect.left;
sizey[i] = MonitorRect.bottom - MonitorRect.top;
i++;

}

sizex and sizey now hold the x and y dimensions of each monitor

Joris Lambrecht
My Contributions: Relative Rotation, Window Sizing