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

思路：

字符串处理

sscanf() – 从一个字符串中读进与指定格式相符的数据
sprintf() – 字符串格式化命令，主要功能是把格式化的数据写入某个字符串中

C++：

#include <iostream>
#include <string.h>
using namespace std;
int main() {
	int n, cnt = 0;
	char a[50], b[50];
	double temp, sum = 0.0;
	cin >> n;
	for(int i = 0; i < n; i++) {
		scanf("%s", a);
		sscanf(a, "%lf", &temp);
		sprintf(b, "%.2lf",temp);
		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 number\n", a);
			continue;
		} else {
			sum += temp;
			cnt++;
		}
	}
	if(cnt == 1) {
		printf("The average of 1 number is %.2lf", sum);
	} else if(cnt > 1) {
		printf("The average of %d numbers is %.2lf", cnt, sum / cnt);
	} else {
		printf("The average of 0 numbers is Undefined");
	}
	return 0;
}