hdu 2080 夹角有多大II

#include<stdio.h>
#include<math.h>
int main()
{
    double x1,y1,x2,y2,k1,k2,pi,k;
    int n;
    scanf("%d",&n);
    pi=atan(1.0)*4;//pi代表圆周率
    while(n--)
    {
        scanf("%lf %lf %lf %lf",&x1,&y1,&x2,&y2);
        if(fabs(x1)<=0.00001&&y1>0) k1=90;//x,y为0的情况，不能把x==0作为判断条件，x,y为实数
        if(fabs(x1)<=0.00001&&y1<0) k1=270;
        if(fabs(x2)<=0.00001&&y2>0) k2=90;
        if(fabs(x2)<=0.00001&&y2<0) k2=270;
        if(fabs(y1)<=0.00001&&x1>0) k1=0;
        if(fabs(y2)<=0.00001&&x1<0) k1=180;
        if(fabs(y2)<=0.00001&&x2>0) k2=0;
        if(fabs(y2)<=0.00001&&x2<0) k2=180;
        if(x1!=0&&y1!=0&&x2!=0&&y2!=0)
        {
        k1=y1/x1;
        k2=y2/x2;
        k1=atan(k1);
        k2=atan(k2);
        k1=k1*180/pi;
        k2=k2*180/pi;}
        k=k1-k2;
        if(k<0) k=-k;//把度数转化到[0,180]
        if(k>180) k=360-k;
        printf("%.2lf\n",k);
    }
    return 0;
}