团体程序设计天梯赛-练习集 L1-017 到底有多二 (15分)

#include <iostream>
using namespace std;
int main()
{
    string s;
    cin >> s;
    int flag = (s[0] == '-' ? 1 : 0);
    int len = s.length();
    int bit = len - flag, cnt = 0;
    for (int i = 0; i < len; i++)
    {
        if (s[i] == '2')
        {
            cnt++;
        }
    }
    double ans = (double)cnt / bit * 100;
    if (flag == 1)
    {
        ans = ans * 1.5;
    }
    if ((s[len - 1] - '0') % 2 == 0)
    {
        ans = ans * 2;
    }
    printf("%.2f%%", ans);
    return 0;
}