HDU 2108 Shape of HDU

#include <cmath>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn = 1e3+10;
#define met(a,b) memset(a,b,sizeof(a))
struct node
{
    int x,y;
}s[maxn];
int get(int a,int b,int c)
{
    int t;
    t=(s[a].x-s[c].x)*(s[b].y-s[c].y)-(s[b].x-s[c].x)*(s[a].y-s[c].y);
    return t;
}
int main()
{
    int n;
    while(scanf("%d",&n)!=EOF&&n!=0)
    {
        for(int i=0;i<n;i++)
            scanf("%d%d",&s[i].x,&s[i].y);
        int t=0;
        for(int i=0;i<n;i++)
        {
            t=get(i%n,(i+1)%n,(i+2)%n);
            if(t<0)
                break;
        }
        if(t>=0)
            printf("convex\n");
        else
            printf("concave\n");
    }
}