Poj 1654--Area(叉积)

#include <cstdio>
#include <cstring>
const int MAXN = 1000001;
char str[MAXN];
int ac[10][2]={0, 0, -1, -1, 0, -1, 1, -1, -1, 0, 0, 0, 1, 0, -1, 1, 0, 1, 1, 1};
int main(){
    int T;
    scanf("%d", &T);
    while(T--){
        scanf("%s", str);
        long long sum = 0;
        int a = ac[str[0]-‘0‘][0];
        int b = ac[str[0]-‘0‘][1];
        for(int i = 1; i < strlen(str); i++){
            int c = a + ac[str[i]-‘0‘][0];
            int d = b + ac[str[i]-‘0‘][1];
            sum += a*d - b*c;
            a = c; b = d;
        }
        if(sum < 0)
            sum = -sum;
        printf("%lld", sum/2);
        if(sum%2)
            printf(".5");
        printf("\n");
    }
    return 0;
}