PAT_A1108#Finding Average

Source:

PAT A 1108 Finding Average (20 分)

Description:

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

Keys:

• 字符串处理
• string（C++ STL）

Attention:

• 小数先相加再乘基数，整数先乘基数再相加
• str.c_str(）函数
• s.size()是unsigned，if（s.size()-pos-1 > 2）这个操作，实际上是无符号整数比较大小，真值的负数会大于正数

Code:

 /*
 Data: 2019-06-16 13:51:57
 Problem: PAT_A1108#Finding Average
 AC: 24:26

 题目大意：
 计算n个数的平均值，合法数范围在[-1000,1000]，且不超过两位小数
 */

 #include<cstdio>
 #include<string>
 #include<iostream>
 using namespace std;

 bool isLegal(string s, double &num)
 {
     int sign=;
     if(s[] == '-')
     {
         sign=-;
         s.erase(,);
     }
     int pos=s.size();
     for(int i=; i<s.size(); i++)
     {
         if(s[i] == '.')
         {
             if(pos==s.size())
                 pos = i;
             else
                 return false;
         }
         else if(s[i]<'' || s[i]>'')
             return false;
     }
     int len = s.size()-pos-;
     if(len > )
         return false;
     num=;
     double upper=,lower=;
     for(int i=; i<pos; i++)
     {
         upper *= ;
         upper += (s[i]-'');
     }
     for(int i=s.size()-; i>pos; i--)
     {
         lower += (s[i]-'');
         lower *= 0.1;
     }
     num = upper + lower;
     if(num > )
         return false;
     num *= sign;
     return true;
 }

 int main()
 {
 #ifdef  ONLINE_JUDGE
 #else
     freopen("Test.txt", "r", stdin);
 #endif // ONLINE_JUDGE

     int n,cnt=;
     string str;
     double sum=,num;
     scanf("%d", &n);
     for(int i=; i<n; i++)
     {
         cin >> str;
         if(isLegal(str,num))
         {
             cnt++;
             sum += num;
         }
         else
             printf("ERROR: %s is not a legal number\n", str.c_str());
     }
     if(cnt==)
         printf("The average of 0 numbers is Undefined");
     else if(cnt==)
         printf("The average of 1 number is %.2f", sum);
     else
         printf("The average of %d numbers is %.2f", cnt,sum/cnt);

     return ;
 }

Update：

 /*
 Data: 2019-08-17 20:23:41
 Problem: PAT_A1108#Finding Average
 AC: 24:26

 题目大意：
 计算n个数的平均值，合法数范围在[-1000,1000]，且不超过两位小数
 */
 #include<cstdio>
 #include<string>
 #include<iostream>
 using namespace std;
 const int Er=1e4;

 double ToF(string s)
 {
     int cnt=,acr=;
     string x="";
     for(int i=; i<s.size(); i++)
     {
         x += s[i];
         if(s[i]=='-' && i==)
             continue;
         if(cnt)
             acr++;
         if(s[i] == '.')
         {
             cnt++;
             if(cnt==)
                 return Er;
         }
         else if(s[i]<'' || s[i]>'')
             return Er;
     }
     if(acr>)
         return Er;
     else
         return atof(x.c_str());
 }

 int main()
 {
 #ifdef ONLINE_JUDGE
 #else
     freopen("Test.txt", "r", stdin);
 #endif // ONLINE_JUDGE

     int n,cnt=;
     double x=,sum=;
     string s;
     scanf("%d", &n);
     for(int i=; i<n; i++)
     {
         cin >> s;
         x = ToF(s);
         if(x>1e3 || x<-1e3)
             printf("ERROR: %s is not a legal number\n", s.c_str());
         else
         {
             sum += x;
             cnt++;
         }
     }
     if(cnt==)
         printf("The average of 0 numbers is Undefined\n");
     else if(cnt==)
         printf("The average of 1 number is %.2f\n", sum);
     else
         printf("The average of %d numbers is %.2f\n", cnt,sum/cnt);

     return ;
 }