View Code of Problem 67

#include<stdio.h>
int main()
{
	double x1,x2,x3,x4,y1,y2,y3,y4;
	while(scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4)!=EOF)
	{
		double k1=-1,k2=0,flag=0;
		if(x1!=x2)
		   k1=(y1-y2)/(x1-x2);
		else
		{
			if(x1==x3&&x3==x4)
			{
				printf("YES\n");
				flag=1;
			}
			else
			{
				printf("NO\n");
				flag=1;
			}
		}
		if(x3!=x4)
		  k2=(y3-y4)/(x3-x4);
	    if(k1==k2)
	      printf("NO\n");
	    else if(k1!=k2&&flag==0)
	      printf("YES\n");
	}
}