C Program :
Given coordinates of three points (x1,y1), (x2,y2) & (x3,y3).
Write a prog. to check if they are collinear.

C Programming -->
 
/* PROG. TO CHECK GIVEN THREE POINTS ARE COLLINEAR OR NOT */
#include<stdio.h>
#include<conio.h>
#include<math.h>
main()
{
int x1,x2,x3,y1,y2,y3;
float d1,d2,d3;
int cl,c2,C3;
clrscr();
printf("enter coordinates ofthree points");
scanf("%d%d%d%d%d%d" ,&x 1,&yl ,&x2,&y2,&x3,&y3);
/* calculate distance between two points */
d1= sqrt( (x1-x2)*(x1-x2) + (yl-y2)*(yl-y2));
d2= sqrt( (x3-x2)*(x3-x2) + (y3-y2)*(y3-y2) );
d3= sqrt( (xl-x3)*(x1-x3) + (y1-y3)*(y1-y3));
/* check the conditions */
cl = ( d1+d2=d3 );
c2= (d2+d3=dl );
c3= (d3+dl==d2);
if(c 111c211c3)
printf(" points are collinear");
else
printf("points are not collinear");
getch();
}