Linerel function draws a line from the current position(CP) to a point that is a relative distance (x, y) from the CP, then advances the CP by (x, y). You can use getx and gety to find the current position.
#include <graphics.h> #include <conio.h> main() { int gd = DETECT, gm; initgraph(&gd, &gm, "C:\\TC\\BGI"); moveto(250, 250); linerel(100, -100); getch(); closegraph(); return 0; }