Pat(A) 1108. Finding Average (20)

原题目：

原题链接：https://www.patest.cn/contests/pat-a-practise/1108

1108. Finding Average (20)

---

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 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

题目大意

给出一系列“数”，求出所有符合要求的数的个数和平均值。
要求是最多精确到小数后两位的数。

解题报告

注意当个数为1和大于1的时候输出是不同的。

代码

#include "iostream"#include "string"#include "cmath"using namespace std;double s2d(string s){    int i,l = s.length();    int flag = 0; // 0: 正数    if(s[0] == '-')        flag = 1;    double num = 0;    int dot = 0;    for(i = flag; i < l; i++){        if(!((s[i] >= '0' && s[i] <= '9') || s[i] == '.'))            return 9999;        if(s[i] == '.'){            if(!dot)                dot ++;            else                return 9999;        }else{            if(dot)                dot ++;            num *= 10;            num += s[i] - '0';        }    }    if(dot > 3)        return 9999;    if(flag)        return (-1) * num/pow(10.0,dot?(dot -1):0);    return num/pow(10.0,dot?(dot -1):0);}int main(){    string s ;    int n,i,cnt = 0;    double sum = 0,x;    cin>>n;    for(i = 0; i < n; i ++){        cin>>s;        x = s2d(s);        if(x >= -1000 && x <= 1000){            cnt ++;            sum += x;        }else            cout<<"ERROR: "<<s<<" is not a legal number"<<endl;    }    if(cnt == 1)        printf("The average of %d number is %.2f\n",cnt,sum/cnt);    else if(cnt)        printf("The average of %d numbers is %.2f\n",cnt,sum/cnt);    else        printf("The average of 0 numbers is Undefined\n");    system("pause");}