Three points fall on one straight line.

 TO CHECK WHETHER THE 3 GIVEN COORDINATES FALL ON ONE STRAIGHT LINE:

include<stdio.h>

int main()
{
    float m,n,x1,x2,x3,y1,y2,y3;
    printf("enter the coordinates x1,y1 = ");
    scanf("%f%f",&x1,&y1);
    printf("\nenter the coordinates x2,y2 = ");
    scanf("%f%f",&x2,&y2);
    printf("\nenter the coordinates x3,y3 = ");
    scanf("%f%f",&x3,&y3);
    m=(y2-y1)/(x2-x1);
    n=(y3-y2)/(x3-x2);
    if(m==n)
    {
        printf("lies on same straight line");
    }
    else
    {
        printf("not lies on same straight line");
    }
    return 0;
}

OUTPUT :

enter the coordinates x1,y1 = 2

3

enter the coordinates x2,y2 = 4

5

enter the coordinates x3,y3 = 6

7

lies on same straight line