PAT--1108 Finding Average

使用cout输出小数点后指定位数用cout << setiosflags(ios::fixed)<< setprecision(2) << a << endl;
当然也可以使用printf("%.2f", a);

#include <iostream>
#include <string>
#include <iomanip>

using namespace std;

bool islegal(string str)
{
    int cnt = 0;
    for(int i = 0; i < str.size(); i++)
    {
        if(isalpha(str[i]))
            return false;
        if(str[i] == '.')
        {
            cnt++;
            //小数点后的位数大于2
            string tmp = str.substr(i+1);
            if(tmp.size() > 2)
                return false;
            if(cnt >= 2)
                return false;
        }
    }
    double tmp = stod(str);
    if(tmp < -1000 || tmp > 1000)
        return false;
    return true;
}

int main()
{
    int n;
    string str;
    while(cin >> n)
    {
        getchar();
        getline(cin, str);
        int j = 0, cnt = 0;
        double sum = 0;
        for(int i = 0; i < str.size(); i++)
        {
            if(str[i] == ' ' || i == str.size()-1)
            {
            	//如果是最后一个字符，要将i++，这样才能截取到完整的最后一个单词
                if(i == str.size()-1) 
                    i++;
                if(islegal(str.substr(j, i-j)))
                {
                    double tmp = stod(str.substr(j, i-j));
                    sum += tmp;
                    cnt++;
                }
                else
                    cout << "ERROR: " << str.substr(j, i-j) <<" is not a legal number" << endl;
                j = i+1;  //下一个单词开始的地方
            }
        }
        if(cnt > 1)
            cout << "The average of " << cnt <<" numbers is " <<setiosflags(ios::fixed)<<setprecision(2) << sum/cnt << endl;
        else if(cnt == 1)
            cout << "The average of 1 number is " << setiosflags(ios::fixed)<<setprecision(2) << sum << endl;
        else
            cout << "The average of 0 numbers is Undefined" << endl;

    }

    return 0;
}