A1108 Finding Average (20 point(s))

sscanf,sprintf使用

1. 原文

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 Nnumbers 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

2. 解析

输入格式判断

sscanf(c,”%lf”,&num); 字符串以浮点数格式赋值给num

sprintf(c,”%.2f”,num); num以字符串格式赋值给字符串

3. AC代码

#include<cstdio>
char c1[1000],c2[1000];
int main()
{
	int n;
	scanf("%d",&n);
	double num=0;
	int cnt=0;
	double sum=0; 
	for (int i = 0; i < n; ++i)
	{
		scanf("%s",c1);
		sscanf(c1,"%lf",&num);
		sprintf(c2,"%.2f",num);
		int flag=0;
		for (int i = 0; c1[i] != '\0'; ++i)
		{
			if (c1[i]!=c2[i])
			{
				flag=1;
				break;
			}
		}
		if (flag==1||(num<-1000||num>1000))
		{
			printf("ERROR: %s is not a legal number\n",c1);
		}else{
			cnt++;
			sum+=num;
		}
	}
	if (cnt==1)
	{
		printf("The average of 1 number is %.2f\n",sum);
	}else if(cnt>1){
        printf("The average of %d numbers is %.2f\n",cnt,sum/cnt);
	}else{
		printf("The average of 0 numbers is Undefined\n");
	}
	return 0;
}