PAT Advanced 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

乙级真题

#include <iostream>
#include <cstring>
using namespace std;
int main()
{
    int N;cin>>N;
    double avg=0;
    int val,coun=0;
    double a;
    while(N--){
        bool right=true;
        char tmp[50],tmp2[50];
        scanf("%s",tmp);
        sscanf(tmp,"%lf",&a);
        sprintf(tmp2,"%.2f",a);
        for(int i=0;i<strlen(tmp);i++)
            if(tmp[i]!=tmp2[i]) right=false;
        if(right&&a<=1000&&a>=-1000) {
            avg+=a;
            coun++;
        }
        else printf("ERROR: %s is not a legal number\n",tmp);
    }
    if(coun!=0) {
        if(coun>1){
            avg/=coun;
            printf("The average of %d numbers is %.2f",coun,avg);
        }else printf("The average of 1 number is %.2f",avg);
    }else printf("The average of 0 numbers is Undefined");

    system("pause");
    return 0;
}