PAT 甲级 1108 Finding Average (20分)

 

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 [−] 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 (≤). 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

AC【找平均数】三部曲：1、[ 判断合法 ] 　　 2、[ 记录合法 ]　　 3、[ 分类输出 ]

#include<bits/stdc++.h>
using namespace std; //legal  [-1000,1000]  2 decimal 

bool isLegal(string &s)
{
    for(int i = 0; i < s.length(); i++) 
    {
        if(s[i] >= 'A' && s[i] <= 'z') return false;
        if(s[i] == '.' && (s.length() - i - 1) > 2) return false;
    }
    double d = stod(s); 
    if(d > 1000 || d < -1000) return false;
    return true;
}

int main()
{// illegal input number, print in a line ERROR: X is not a legal number
    int n, cnt = 0; cin >> n;
    string s; double total = 0.0;
    
    for(int i = 0; i < n; i++)
    {
        cin >> s;
        if(isLegal(s))
        {
            cnt++; double d = stod(s);
            total += d;
        }
        else cout << "ERROR: " << s << " is not a legal number" << endl;
    }
    
    if(cnt == 0) cout << "The average of 0 numbers is Undefined";
    else if(cnt == 1) printf("The average of 1 number is %.2lf", total);
    else printf("The average of %d numbers is %.2lf", cnt, total/cnt);
 
    return 0;
}

Tips :　　

int num = stoi(s); 　　　　　　// string 转 int
double num = stod(s); 　　　  // string 转 float
float num = stof(s); 　　　　   // string 转 double
string s = to_string(num); 　   //  int 转 string

bool isLegal(string &s)　　　 //判断 string 是否合法（符合题意）
{
　　for(int i = 0; i < s.length(); i++)
　　{
　　　　if(s[i] >= 'A' && s[i] <= 'z') return false;
　　　　if(s[i] == '.' && (s.length() - i - 1) > 2) return false;
　　}
　　double d = stod(s);
　　if(d > 1000 || d < -1000) return false;
　　return true;
}

 "只要你不停止，走慢一点没关系"