View Code of Problem 67

#include<stdio.h>

int main() {
	float x1, x2, x3, x4, y1, y2, y3, y4, k1, k2;
	while(scanf("%f %f %f %f", &x1, &y1, &x2, &y2) != EOF) {
		scanf("%f %f %f %f", &x3, &y3, &x4, &y4);
		if(x1 == x2 && x3 == x4 && x1 != x3) {
			printf("No\n");
		}
		else if(x1 != x2 && x3 != x4) {
			k1 = (y2 - y1) / (x2 - x1);
			k2 = (y4 - y3) / (x4 - x3);
			if(k1 != k2)
				printf("Yes\n");
			else {
				if(y1-k1*x1 == y3-k2*x3)
					printf("Yes\n");
				else
					printf("No\n");
			}
		}
		else 
			printf("Yes\n");
	}
	return 0;
}