1108 Finding Average (20 分)字符串处理（sscanf和sprintf)

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

题意：先输入一个整数n，再输入n个数，判断他们合不合法
思路：使用sscanf和sprintf函数

#include
#include
#include 
#include
#include
#include
#include
#include
#include
#include
#include

using namespace std;

int main() {
	int n,cnt = 0;
	scanf("%d",&n);
	char a[50],b[50];
	double temp,sum = 0.0;
	for(int i = 0;i < n;i++) {
		cin >> 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 == 1 || temp < -1000 || temp > 1000) {
			printf("ERROR: %s is not a legal number\n",a);
			continue;
		} else {
			sum = 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;
}