题目链接：https://pintia.cn/problem-sets/994805342720868352/problems/994805360777347072
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 长度为1时，如果它不是数字，则不合法。如果字符串中有除了0-9、‘-’、‘.’之外的字符，则不合法。
‘-’只能有一个，且不能位于开头，‘.’只能有一个，wa的点在于数据中的小数点是可以放在开头的。
判断结束后，将字符转化为数字，如果有小数点，分小数点前后计算得到数字。
如果数字范围不在-1000~1000，则不合法，最后输出其平均值，注意只有1个数字合法时，输出的为‘number’
for(int i=0;i<pos;i++){
if(a[i]=='-'){
continue;
}else{
ans1=ans1*10+(a[i]-'0');
}
}
for(int i=len-1;i>pos;i--){
ans2=(ans2+a[i]-'0')/10.0;
}
double ans=ans1+ans2;
}#include<iostream>
#include<cstring>
using namespace std;
int main(){
char a[1111];
double sum=0.0;
double cnt=0;
int n;
cin>>n;
while(n--){
cin>>a;
int len=strlen(a);
if(len==1){
if(a[0]<'0'||a[0]>'9'){
printf("ERROR: %s is not a legal number\n",a);
continue;
}
}
int f=0;
for(int i=0;i<len;i++){
if(a[i]!='.'&&a[i]!='-'&&(a[i]<'0'||a[i]>'9')){
f++;
}
}
if(f>0){
printf("ERROR: %s is not a legal number\n",a);
continue;
}
int cnt1=0,cnt2=0,pos=-1;
for(int i=0;i<len;i++){
if(a[i]=='-'){
cnt1++;
}
if(a[i]=='.'){
cnt2++;
pos=i;
}
}
if(cnt1>=2){
printf("ERROR: %s is not a legal number\n",a);
continue;
}else if(cnt1==1){
if(a[0]!='-'){
printf("ERROR: %s is not a legal number\n",a);
continue;
}
}
if(cnt2>=2){
printf("ERROR: %s is not a legal number\n",a);
continue;
}
else if(cnt2==1){
if(pos<=len-4){
printf("ERROR: %s is not a legal number\n",a);
continue;
}
}
double ans1=0,ans2=0;
if(cnt2==0){
pos=len;
}
for(int i=0;i<pos;i++){
if(a[i]=='-'){
continue;
}else{
ans1=ans1*10+(a[i]-'0');
}
}
for(int i=len-1;i>pos;i--){
ans2=(ans2+a[i]-'0')/10.0;
}
double ans=ans1+ans2;
if(a[0]=='-'){
ans=-ans;
}
if(ans>1000||ans<-1000){
printf("ERROR: %s is not a legal number\n",a);
continue;
}else{
cnt++;
sum+=ans;
}
}
if(cnt==0){
printf("The average of 0 numbers is Undefined\n");
}else if(cnt==1){
printf("The average of 1 number is %.2lf\n",sum);
}else{
sum/=cnt;
printf("The average of %.0lf numbers is %.2lf\n",cnt,sum);
}
return 0;
}