【刷题-PAT】A1108 Finding Average （20 分）

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 [−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 Kis 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

分析：使用sscanf()和sprintf()函数即可

#include<iostream>
#include<cstdio>
#include<cstring>
#include<vector>
#include<string>
#include<unordered_map>
#include<set>
#include<queue>
#include<algorithm>
#include<cmath>
using namespace std;
int main(){
    #ifdef ONLINE_JUDGE
    #else
    freopen("input.txt", "r", stdin);
    #endif // ONLINE_JUDGE
    int n = 0;
    scanf("%d", &n);
    int cnt = 0;
    double sum = 0, num;
    for(int i = 0; i < n; ++i){
        char str[100], t[100];
        scanf("%s", str);
        sscanf(str, "%lf", &num);
        sprintf(t, "%.2f", num);
        bool flag = true;
        //写入失败时，写入的地方存的还是之前的内容，所以要比较
        for(int i = 0; i < strlen(str); ++i){
            if(str[i] != t[i])flag = false;
        }
        if(flag == false || abs(num) > 1000){
            printf("ERROR: %s is not a legal number
", str);
        }else{
            cnt++;
            sum += num;
        }
    }
    if(cnt == 0){
        printf("The average of 0 numbers is Undefined
");
    }else if(cnt == 1){
        printf("The average of 1 number is %.2lf
", sum);
    }else{
        printf("The average of %d numbers is %.2lf
", cnt, sum / cnt);
    }
    return 0;
}