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,k2;
	    if(x1==x2&&x3==x4)
	    {
	    	if(x1==x3)
	    	 printf("Yes\n");
	    	else 
	    	 printf("No\n");
		}
		else 
		{
			k1=(y1-y2)/(x1-x2);
			k2=(y3-y4)/(x3-x4);
			double b1,b2;
			b1=y1-k1*x1;
			b2=y3-k2*x3;
			if(k1==k2&&b1!=b2)//两线段平行 
			  printf("No\n");
			else 
			  printf("Yes\n");
		}   
	}
}