【PAT】【Advanced Level】1108. Finding Average (20)

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解决PAT-A 1108 Finding Average题目，介绍合法数字验证及平均数计算的方法，使用C++实现，涉及sscanf和sprintf函数的学习。

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1108. Finding Average (20)

时间限制

400 ms

内存限制

65536 kB

代码长度限制

16000 B

判题程序

Standard

作者

CHEN, Yue

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

原题链接：

https://www.patest.cn/contests/pat-a-practise/1108

思路：

学习新函数：sscanf，sprintf

https://www.cnblogs.com/xmxu/archive/2012/08/20/2647386.html

https://www.cnblogs.com/gmh915/archive/2009/09/30/1576995.html

CODE：

#include<iostream>
#include<cstring>
#include<string>
#include<cmath>
#include<cstdlib>
#include<cstdio>
using namespace std;

int main()
{
	int n;
	cin>>n;
	int fl=0;
	double sum=0;
	for (int i=0;i<n;i++)
	{
		char a[50],b[50];
		cin>>a;
		double temp;
		sscanf(a,"%lf",&temp);
		sprintf(b,"%.2f",temp);
		int flag=0;
		for (int i=0;i<strlen(a);i++)
		{
			if (a[i]!=b[i])
			{
				flag=1;
				break;
			}
		}
		if(flag==1 || temp<-1000 || temp>1000)
		{
			cout<<"ERROR: "<<a<<" is not a legal number"<<endl;
		}
		else
		{
			fl++;
			sum+=temp;
		}
	}	
	if (abs(sum-0)<0.005) sum=0;
	if (fl==0)
	{
		printf("The average of 0 numbers is Undefined");
	}
	else if (fl==1)
	{
		printf("The average of 1 number is %.2lf",sum);
	}
	else
	{
		printf("The average of %d numbers is %.2lf",fl,sum/fl);
	}
	return 0;
}