old/ASM/swap/sw.c

void main()
{
 char a=1,b=2;
 asm {
   mov al,a;
   xchg al,b;
   mov a,al;
   mov dl,a;
   add dl,0x30;
   mov ah, 2;
   int 0x21;
   mov dl,b;
   add dl,0x30;
   int 0x21;
 }
}