poj 2190 ISBN

<pre >#include <iostream>#include <cstdlib>#include <cstring>#include <cstdio>using namespace std;char st[20];int main(){    gets(st);    int ans = 0;    int pos = 0;    for (int i = 0; i < 10; i++)        if (st[i] == '?') pos = 10 - i;        else if (st[i] == 'X') ans += 10 * (10 - i);        else ans += (st[i] - '0') * (10 - i);    for (int i = 0; i <= 9; i++)        if ((ans + i * pos) % 11 == 0)        { printf("%dn", i); return 0;        }    if ((ans + 10 * pos) % 11 == 0 && pos == 1)    {        printf("Xn");        return 0;    }    printf("-1n");    return 0;}