题目：https://pintia.cn/problem-sets/994805342720868352/problems/994805360777347072
基本一遍过，题意理解有点问题
注意count = 1时，输出的是number

代码

  1. #include <cstdio>
  2. #include <string>
  3. #include <iostream>
  4. using namespace std;
  6. bool judge(string str){
  7.     int dotcount = 0;
  8.     for(int i = 0; i < str.size(); i++){
  9.         if(!((str[i] >= '0' && str[i] <= '9')|| str[i] == '.' || str[i] == '-')){
  10.             return false;
  11.         }
  12.         else if(str[i] == '.'){
  13.             if(str.size() - i > 3) return false;
  14.             dotcount++;
  15.             if(dotcount > 1) return false;
  16.         }
  17.     }
  18.     if(stod(str) > 1000.0 || stod(str) < -1000.0) return false;
  19.     return true;
  20. }
  22. int main(){
  23.     int n, count = 0;
  24.     double sum = 0.0;
  25.     string input;
  26.     scanf("%d", &n);
  27.     for(int i = 0; i < n; i++){
  28.         cin>>input;
  29.         if(judge(input)){
  30.             count++;
  31.             sum += stod(input);
  32.         } else {
  33.             cout<<"ERROR: "<<input<<" is not a legal number"<<endl;
  34.         }
  35.     }
  36.     if(count == 0){
  37.         printf("The average of 0 numbers is Undefined");
  38.     } else if(count == 1){
  39.         printf("The average of 1 number is %.2f", sum/count);
  40.     }
  41.     else {
  42.         printf("The average of %d numbers is %.2f", count, sum/count);
  43.     }
  44.     return 0;
  45. }