**Why DDA algorithm ?**

DDA Algorithm is used to plot line between two nodes i.e two end points in computer system.

While our computer understand pixels, if we want to plot a line, we should have maximum intermediate vertices of the line i.e intermediate points, so as to generate a straight line. Here DDA does the same.

code#include <graphics.h> #include <stdio.h> #include <math.h> int main( ) { float x,y,x1,y1,x2,y2,dx,dy,pixel; int i,gd,gm; printf("Enter the value of x1 : "); scanf("%f",&x1); printf("Enter the value of y1 : "); scanf("%f",&y1); printf("Enter the value of x2 : "); scanf("%f",&x2); printf("Enter the value of y1 : "); scanf("%f",&y2); detectgraph(&gd,&gm); initgraph(&gd,&gm,""); dx=abs(x2-x1); dy=abs(y2-y1); if(dx>=dy) pixel=dx; else pixel=dy; dx=dx/pixel; dy=dy/pixel; x=x1; y=y1; i=1; while(i<=pixel) { putpixel(x,y,1); x=x+dx; y=y+dy; i=i+1; delay(100); } getch(); closegraph(); }

**DDA algorithm :**

- Define the nodes, i.e end points in form of (x1,y1) and (x2,y2).
- Calculate the distance between the two end points vertically and horizontally, i.e dx=|x1-x2| and dy=|y1-y2|.
- Define new variable name ‘pixel’, and compare dx and dy values,

if dx > dy then

pixel=dx

else

pixel =dy. - dx=dx/pixel

and dy=dy/pixel - x=x1;

y=y1; - while (i<=pixel) compute the pixel and plot the pixel with x=x+dx and y=y+dy.