## Pat(A) 1108. Finding Average (20)

### 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

### 代码

#include "iostream"
#include "string"
#include "cmath"
using namespace std;

double s2d(string s){
int i,l = s.length();
int flag = 0; // 0: 正数
if(s[0] == '-')
flag = 1;
double num = 0;
int dot = 0;
for(i = flag; i < l; i++){
if(!((s[i] >= '0' && s[i] <= '9') || s[i] == '.'))
return 9999;
if(s[i] == '.'){
if(!dot)
dot ++;
else
return 9999;
}else{
if(dot)
dot ++;
num *= 10;
num += s[i] - '0';
}
}
if(dot > 3)
return 9999;
if(flag)
return (-1) * num/pow(10.0,dot?(dot -1):0);
return num/pow(10.0,dot?(dot -1):0);
}

int main(){
string s ;
int n,i,cnt = 0;
double sum = 0,x;
cin>>n;
for(i = 0; i < n; i ++){
cin>>s;
x = s2d(s);
if(x >= -1000 && x <= 1000){
cnt ++;
sum += x;
}else
cout<<"ERROR: "<<s<<" is not a legal number"<<endl;
}
if(cnt == 1)
printf("The average of %d number is %.2f\n",cnt,sum/cnt);
else if(cnt)
printf("The average of %d numbers is %.2f\n",cnt,sum/cnt);
else
printf("The average of 0 numbers is Undefined\n");
system("pause");
}

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