PAT 1108 Finding Average

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

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;


int main(){
    int n,cnt = 0;
    cin >> n;
    char a[50],b[50];
    double temp,sum = 0.0;
    for(int i=0;i < n;i++){
        scanf("%s",a);
        sscanf(a,"%lf",&temp);  //格式和scanf差不多，从a输入到temp  temp加&
        sprintf(b,"%.2f",temp); //从temp输出到b
        int flag = 0;
        for(int j=0;j < strlen(a);j++)if(a[j]!=b[j])flag = 1;

        if(flag||temp < -1000||temp > 1000){
            printf("ERROR: %s is not a legal numbern",a);
            continue;
        }
        else{
            sum += temp;
            cnt++;
        }
    }

    if(cnt == 1)printf("The average of 1 number is %.2f",sum);
    else if(cnt > 1)printf("The average of %d numbers is %.2f",cnt,sum / cnt);
    else printf("The average of 0 numbers is Undefined");

    return 0;
}

sscanf 和 sprintf！！学到了