PTA Finding Average (20 分)

It is the human mind that releases infinite light, and it is also the human mind that creates boundless darkness. Light and darkness are intertwined and fight together. This is the world for which we are nostalgic and helpless.

The basic task is simple: given N real numbers, you are supposed to calculate their average. But what makes it complicated is that some of the input numbers might not be legal. A legal input is a real number in [−1000,1000] and is accurate up to no more than 2 decimal places. When you calculate the average, those illegal numbers must not be counted in.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤100). Then N numbers are given in the next line, separated by one space.

Output Specification:

For each illegal input number, print in a line ERROR: X is not a legal number where X is the input. Then finally print in a line the result: The average of K numbers is Y where K is the number of legal inputs and Y is their average, accurate to 2 decimal places. In case the average cannot be calculated, output Undefined instead of Y. In case K is only 1, output The average of 1 number is Y instead.

Sample Input 1:

7
5 -3.2 aaa 9999 2.3.4 7.123 2.35

Sample Output 1:

ERROR: aaa is not a legal number
ERROR: 9999 is not a legal number
ERROR: 2.3.4 is not a legal number
ERROR: 7.123 is not a legal number
The average of 3 numbers is 1.38

Sample Input 2:

2
aaa -9999

Sample Output 2:

ERROR: aaa is not a legal number
ERROR: -9999 is not a legal number
The average of 0 numbers is Undefined

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <vector>
#include <ctime>
#include <cctype>
#include <bitset>
#include <utility>
#include <sstream>
#include <complex>
#include <iomanip>
#include<climits>//INT_MAX
//#include<bits/stdc++.h>
#define PP pair<ll,int>
#define inf 0x3f3f3f3f
#define llinf 0x3f3f3f3f3f3f3f3fll
#define dinf 1000000000000.0
#define PI 3.1415926
typedef long long ll;
using namespace std;
int const mod=1e9+7;
const int maxn=1010;
int n,ct=0;
double sum=0;
int main(){
    //ios::sync_with_stdio(false);
    //cin.tie(NULL);
    //cout.tie(NULL);
    cin>>n;
    for(int i=1;i<=n;++i){
        string s;
        cin>>s;
        int fg=0,dd=-1;
        double x=0;
        if(s[0]=='-')
            fg=1;
        for(int i=fg;i<s.size();++i){
            if(s[i]=='.'){
                dd=i;
                break;
            }
            if(s[i]<'0'||s[i]>'9'){
                fg=2;
                break;
            }
            x*=10;
            x+=s[i]-'0';
        }
        if(dd!=-1)
            for(int i=dd+1;i<s.size();++i){
                if(s[i]<'0'||s[i]>'9'){
                    fg=2;
                    break;
                }
                x+=(s[i]-'0')/(1.0*pow(10,(i-dd)));
            }
        if(fg)
            x*=-1;
        if(s.size()-1-dd>2&&dd!=-1)
            fg=2;
        if(fg==0&&dd==0||fg==1&&dd==1)
            fg=2;
        if(x>1000||x<-1000)
            fg=2;
        if(fg==2){
            cout<<"ERROR: "<<s<<" is not a legal number\n";
            continue;
        }
        ct++;
        sum+=x;
    }
    sum/=1.0*ct;
    cout<<"The average of "<<ct;
    if(ct!=1)
        cout<<" numbers is ";
    else
        cout<<" number is ";
    if(!ct)
        cout<<"Undefined";
    else
        printf("%.2f",sum);
    return 0;
}