HDU 1202 The calculation of GPA

http://acm.hdu.edu.cn/showproblem.php?pid=1202

刚开始没看到输入实数。。。汗、、、

#include <stdio.h>

int main()
{
    double s[100],p[100];
    int n,i;
    double ss,sp;
    int cnt;
    while(~scanf("%d",&n))
    {
        cnt=ss=sp=0;
        for(i=0;i<n;i++)
        {
            scanf("%lf%lf",s+i,p+i);
            if(p[i]==-1){cnt++;continue;}
            ss+=s[i];
            if(p[i]>=90)sp+=4*s[i];
            else if(p[i]>=80)sp+=3*s[i];
            else if(p[i]>=70)sp+=2*s[i];
            else if(p[i]>=60)sp+=s[i];
        }
        if(cnt==n||sp==0)printf("-1\n");
        else
            printf("%.2lf\n",sp/ss);
    }
    return 0;
}