c - how to create a union -

i made mistake while using union,and don't know why. problem in function goto_xy(); read book, cannot compiled. in function trying locate cursor, regs variable not declared. want know function.

#include<stdio.h> #include<windows.h> #include<dos.h> #include<conio.h>  void goto_xy(int x,int y);                         //goto key word;define subfunction creat original cursor int coordinate system void rectangle_clear(int x1,int x2,int y1,int y2); //define rectangle_clear opening subfunction  void center_clear(int x1,int x2,int y1,int y2);    //define center_clear opening subfunction void creat();                                  //define subfunction of creating star int main()                                             //the main function {     creat();     getch();     center_clear(0,25,0,79);     getch(); } void center_clear(int x1,int x2,int y1,int y2)     //the subfunction creats stars while opening project {     int x00,y00,x0,y0,i,d;     if((y2-y1)>(x2-x1))     {         d=(x2-x1)/2;         x0=(x1+x2)/2;         y0=y1+d;         y00=y2-d;         for(i=0;i<(d+1);i++)         {             rectangle_clear((x0-i),(x00+i),(y0-i),(y00+i));         }         delay(10);                                  //to delay dismis of star     }     else     {         d=(y2-y1)/2;         y0=(y1+y2)/2;         x0=x1+d;         x00=x2-d;         for(i=0;i<d+1;i++)         {             rectangle_clear((x0-i),(x00+i),(y0-i),(y00+i));         }         delay(10);     } } void rectangle_clear(int x1,int x2,int y1,int y2)   //to creat star int shape of rectangle {     int i,j;     for(i=y1;i<y2;i++)     {         goto_xy(x1,i);         putchar(' ');         goto_xy(x2,i);         putchar(' ');         delay(10);     }     for(j=x1;j<x2;j++)     {         goto_xy(i,y1);         putchar(' ');         goto_xy(i,y2);         putchar(' ');         delay(10);     } } void goto_xy(int x,int y) {     union regs r;      r.h.ah=2;     r.h.dl=y;     r.h.dh=x;     r.h.bh=0;     int86(0x10,&r,&r); } void creat() {     int i,j;     for(i=0;i<24;i++)     {         for(j=0;j<79;j++)         {             goto_xy(i,j);             printf("a");         }     } } 

it appears me union regs must present in 1 of header files , including same.

as can seen code below, members of union h , members of h present, means union there in header file , including it.

void goto_xy(int x,int y) {     union regs r;      r.h.ah=2; //here accessing member of regs , sub-members of h     r.h.dl=y;     r.h.dh=x;     r.h.bh=0;     int86(0x10,&r,&r); } 

edit: google search tells me union regs defined in dos.h , like

union regs {   struct wordregs x;  struct byteregs h; }; 

so, need include dos.h solve problem. but, appears inspite of including that, problem present. can open dos.h , check if union regs present or not.

see here more details.