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

柔光的暖阳◎ 2024-04-17 21:23 57阅读 0赞

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：**把合法的数字加起来算平均值，合法:\[-1000，1000\]的最多两位小数的数。

发现了一个神奇的东西！sscanf和sprintf 格式化！省去了很多判断！

sscanf与scanf等价，所不同的是，前者的输入字符来源于字符串s，而scanf以stdin作为输入源。

sscanf("123456 ", "%4s", buf); 取指定长度的字符串

取到指定字符为止的字符串。如在下例中，取遇到空格为止字符串。  
　　sscanf("123456 abcdedf", "%\[^ \]", buf);  
　　printf("%s\\n", buf);  
　　结果为：123456

sprintf(s, "%d", 123); //产生"123"

更多用法：[https://www.cnblogs.com/wangtianxj/archive/2009/07/04/1516646.html][https_www.cnblogs.com_wangtianxj_archive_2009_07_04_1516646.html]

#include<stdio.h>
    #include<string.h>
    #include<math.h>
    #include<iostream>
    using namespace std;
    int main()
    {
    	int n,i,j,l,sum=0;//sum 合法数 
    	double s=0,temp;
    	char a[105],b[105];
    	scanf("%d",&n);
    	for(i=0;i<n;i++)
    	{
    		int f=0;
    		scanf("%s",a);
    		sscanf(a,"%lf",&temp);
    		sprintf(b,"%.2f",temp);
    		//cout<<a<<" "<<b<<" "<<temp<<endl;
    		for(int j=0;j<strlen(a);j++)
    		{
    		     if(a[j]!=b[j]) f=1;
    		}
    		if(f||temp<-1000|| temp>1000)
    		{
    		    printf("ERROR: %s is not a legal number\n",a);
    		    continue;
    		}
    		else
    		{
    		    s+=temp;
    		    sum++;
    		}
    	}
    	if(sum==0)
    	printf("The average of 0 numbers is Undefined\n");
    	else if(sum==1)
    	printf("The average of 1 number is %.2lf\n",s/sum);
    	else
    	printf("The average of %d numbers is %.2lf\n",sum,s/sum);
    }

[https_www.cnblogs.com_wangtianxj_archive_2009_07_04_1516646.html]: https://www.cnblogs.com/wangtianxj/archive/2009/07/04/1516646.html