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

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

 1 #include<bits/stdc++.h>
 2 using namespace std; //legal  [-1000,1000]  2 decimal 
 3 
 4 bool isLegal(string &s)
 5 {
 6     for(int i = 0; i < s.length(); i++) 
 7     {
 8         if(s[i] >= 'A' && s[i] <= 'z') return false;
 9         if(s[i] == '.' && (s.length() - i - 1) > 2) return false;
10     }
11     double d = stod(s); 
12     if(d > 1000 || d < -1000) return false;
13     return true;
14 }
15 
16 int main()
17 {// illegal input number, print in a line ERROR: X is not a legal number
18     int n, cnt = 0; cin >> n;
19     string s; double total = 0.0;
20     
21     for(int i = 0; i < n; i++)
22     {
23         cin >> s;
24         if(isLegal(s))
25         {
26             cnt++; double d = stod(s);
27             total += d;
28         }
29         else cout << "ERROR: " << s << " is not a legal number" << endl;
30     }
31     
32     if(cnt == 0) cout << "The average of 0 numbers is Undefined";
33     else if(cnt == 1) printf("The average of 1 number is %.2lf", total);
34     else printf("The average of %d numbers is %.2lf", cnt, total/cnt);
35  
36     return 0;
37 }

View Code