PAT甲级 1108 Finding Average (20 分)

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该程序接收一组数值输入，并检查它们是否合法（在[-1000,1000]范围内且最多两位小数）。非法输入会被标记并排除在平均数计算之外。最后，程序会根据合法输入的数量和值计算并输出平均数，精确到小数点后两位。如果合法输入为0，则输出'Undefined'，如果合法输入为1，则输出单个数值的平均数。

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

#include <iostream>

using namespace std;

int main() {
    int n, k = 0;
    cin >> n;
    string s;
    double sum = 0;
    for (int i = 0; i < n; ++i) {
        cin >> s;
        bool flag = true;
        bool flag1 = true;
        int g = 0;
        if (s[0] == '-')
            g = 1;
        for (int j = g; j < s.size(); ++j) {
            if (s[j] == '.') {
                flag1 = false;
            }
            if (isalpha(s[j])) {
                if (s[j] != '.' or !flag1)
                    flag = false;
                break;
            }
            if (s[j] == '.' and s.size() - j - 1 > 2) {
                flag = false;
                break;
            }
        }
        if (flag) {
            if (stod(s) <= 1000 and stod(s) >= -1000) {
                sum += (s != "" ? stod(s) : 0);
                k++;
            } else
                flag = false;
        }
        if (!flag)
            cout << "ERROR: " << s << " is not a legal number" << endl;
    }
    if (k > 1)
        printf("The average of %d numbers is %.2f", k, sum / k);
    else if (!k)
        printf("The average of 0 numbers is Undefined");
    else
        printf("The average of 1 number is %.2f", sum);
    return 0;
}

#include <iostream>
#include <cstring>

using namespace std;

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