#include <graphics.h>
void line(int x1, int y1, int x2, int y2);
 

line draws a line in the current color, using the current line style and
thickness between the two points specified, (x1,y1) and (x2,y2), without
updating the current position (CP).

/* line example */
 
#include <graphics.h>
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>
 
int main(void)
{
 
   /* request autodetection */
   int gdriver = DETECT, gmode, errorcode;
   int xmax, ymax;
 
   /* initialize graphics and local variables */
   initgraph(&gdriver, &gmode, "");
 
   /* read result of initialization */
   errorcode = graphresult();
 
   if (errorcode != grOk) { /* an error occurred */
printf("Graphics error: %s\n", grapherrormsg(errorcode));
 
printf("Press any key to halt:");
getch();
exit(1);
   }
 
   setcolor(getmaxcolor());
   xmax = getmaxx();
   ymax = getmaxy();
 
   /* draw a diagonal line */
   line(0, 0, xmax, ymax);
 
   /* clean up */
   getch();
   closegraph();
   return 0;
}

getlinesettings linerel lineto setcolor setlinestyle setwritemode

  no output of example at the moment
  do not hesitate and add it...