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 Undefinedinstead 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

#include<iostream>
#include<cstring>

int main(){
    int n;
    scanf("%d",&n);
    double temp,sum = 0.0;
    int cnt = 0;
    char a[50],b[50];
    for(int i = 0 ; i < n; i++){
        scanf("%s",a);
        sscanf(a,"%lf",&temp);
        sprintf(b,"%.2f",temp);
        bool flag = true;
        for(int j = 0; j < strlen(a); j++){
            if(a[j] != b[j]){
                flag = false;
                break;
            }
        }
        if(flag && temp <= 1000 && temp >= -1000){
            cnt++;
            sum += temp;
        }else{
            printf("ERROR: %s is not a legal number\n",a);
        }
    }
    if(cnt == 0){
        printf("The average of 0 numbers is Undefined\n");
    }else if(cnt == 1){
        printf("The average of 1 number is %.2f",sum);
    }else{
        printf("The average of %d numbers is %.2f",cnt,sum/cnt);
    }
    return 0;
}