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)

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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

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#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");
}