C Program to display a line graph using midpoint line algorithm.

#include<stdio.h>
#include<graphics.h>
#include<stdlib.h>
#include<conio.h>
 
#define MAX 20
 
void swap(int* a,int* b)
{
int t=*a;
*a=*b;
*b=t;
}
 
void midpointline(int x1,int y1,int x2,int y2)
{
int dx,dy,d,incry,incre,incrne,slopegt1=0;
dx=abs(x1-x2);dy=abs(y1-y2);
if(dy>dx)
{
swap(&x1,&y1);
swap(&x2,&y2);
swap(&dx,&dy);
slopegt1=1;
}
if(x1>x2)
{
swap(&x1,&x2);
swap(&y1,&y2);
}
if(y1>y2)
incry=-1;
else
incry=1;
d=2*dy-dx;
incre=2*dy;
incrne=2*(dy-dx);
while(x1<x2)
{
if(d<=0)
d+=incre;
else
{
d+=incrne;
y1+=incry;
}
x1++;
if(slopegt1)
putpixel(y1,x1,WHITE);
else
putpixel(x1,y1,WHITE);
}
}
 
void main()
{
int n,i;
int pt[MAX][2];
int gd=DETECT,gm;
 
printf("Enter the number of points:");
scanf("%d",&n);
 
printf("Enter the x and y coordinates:");
for(i=0;i<n;i++)
{
scanf("%d %d",&pt[i][0],&pt[i][1]);
pt[i][1]=480 - pt[i][1];
}
 
initgraph(&gd,&gm,"..\\bgi");
 
line(1,0,1,480);		// X - Axis
line(0,479,639,479);		// Y - Axis
 
outtextxy(pt[0][0]-2,pt[0][1]-3,"*");
 
for(i=0;i<n-1;i++)
{
midpointline(pt[i][0],pt[i][1],pt[i+1][0],pt[i+1][1]);
outtextxy(pt[i+1][0]-2,pt[i+1][1]-3,"*");
}
getch();
closegraph();
}