#include <geos.h>#include <conio.h>#include <stdlib.h>unsigned char x,y;void_func oldMouseVector, oldKeyVector;void foo1 (void) {    // do something on mouse press/release    gotoxy(x,y);    ++x;    cputc('A');    // call previous routine    oldMouseVector();}void foo2 (void) {    // do something on key press/release    gotoxy(x,y);    ++y;    cputc('B');    // call previous routine    oldKeyVector();}void hook_into_system(void) {    // hook into system vectors - preserve old value    oldMouseVector = mouseVector;    mouseVector = foo1;    oldKeyVector = keyVector;    keyVector = foo2;}void remove_hooks(void) {    mouseVector = oldMouseVector;    keyVector = oldKeyVector;}int main(void) {    x = 0;    y = 0;/*    To make cc65 do something for you before exiting you might register    a function to be called using atexit call. #include <stdlib.h> then and    write:*/    atexit(&remove_hooks);    clrscr();    cputsxy(0,1, CBOLDON "Just" COUTLINEON  "a " CITALICON "string." CPLAINTEXT );    hook_into_system();/* This program will loop forever though */    MainLoop();/*    If not using atexit() you have to remember about restoring system vectors    right before exiting your application. Otherwise the system will most    likely crash.    remove_hooks();*/    return 0;}