title: text editor in c using video memory
body: <p>I am creating text editor using C. Can you explain these macros?</p>
  
  <pre><code>#define Ad (unsigned char far *)0xb8000000
  #define Pos(y,x) (2*((y)*80+x))
  #define Write(y,x,ch) *(Ad+Pos(y,x))=ch
  #define WriteA(y,x,fb) *(Ad+1+Pos(y,x))=fb
  </code></pre>