View Code of Problem 67

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