Pat b1054 average (20 points)

1054 averaging (20 branch )

The basic requirements of this question are very simple ： Given N A real number , Calculate their average . But the complexity is that some of the input data may be illegal . One “ legal ” The input is [−1000,1000] The real number in the interval , And at most accurate to the decimal point 2 position . When you calculate the average , You can't count those illegal data .

Input format ：

Enter the first line to give a positive integer N（≤100）. The next line shows N A real number , Numbers are separated by a space .

Output format ：

For every illegal input , Output in one line ERROR: X is not a legal number, among X It's input . Finally, output the result in one line ：The average of K numbers is Y, among K Is the number of legal inputs ,Y It's their average , Accurate to the decimal point 2 position . If the average cannot be calculated , Then use Undefined Replace Y. If K by 1, The output The average of 1 number is Y.

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

For this question , It's the longest question I've spent so far , Now recall , It's really a bit annoying . For output , A number is singular when it is legal number, In other cases numbers, At first, I didn't read the questions carefully , All output numbers, Another half day , But in the end, the code I wrote passed only three test data , There's another one that doesn't work .

Finally, I read other people's blogs , He sent Liu Shen's code , Have to say sscanf and sprintf Function when processing some strings , It really works .

I finally read other people's blogs , I wrote three codes , Summed up a few points ：

• For a relatively complex situation , It is better to write a function , Many of the same situations can be merged , Such as , This question , Return the data that does not conform to the meaning of the question false, Others will return true. All of them are written in the main function , It is possible to omit , From the beginning of the first code, I missed the innermost if sentence , No consideration is given to greater than 1000 Or less than -1000 The situation of .
• else if(flag==1)
              {
                  double dou=str_dou(str);
                  if(i-j<=3)
                  {
                      if(dou>=-1000&&dou<=1000)
                      {
                          ++count;
                          average+=dou;
                      }
                      else
                          ans.push_back(str);
                  }
• It works string Just use string, Don't use tradition c character string , Because sometimes we don't know how big a string to use , Take this question for example . At the beginning of this question, I used the size of 20 Character number of , Thinking about 20 It must be able to hold every data , As a result, a set of data can not pass , puzzled , Finally, the size of the array is changed to 50 Just passed . Be careful. I can't stand it .
• Although only this question took me a lot of time , But it's worth it , After all, I have gained something . Before I finally changed the code , Submit when you see everything right , A feeling of joy welled up in my heart .

Don't talk much , Put it in code. ！！！

This is what I wrote first , Not right at first , The following changes are correct . Now look at it. , It's really complicated .

#include <iostream>
#include <vector>
#include <string>
#include <cstdio>
using namespace std;
double str_dou(string s);

int main()
{
    int n;
    cin >> n;
    string str;
    double average=0;
    int count=0;        //count Statistics of legal data 
    vector<string> ans; //ans Storing illegal data 
    while(n--)
    {
        cin >> str;
        int i,j=0, flag=0;      //j and flag Record the position and number of decimal points respectively 
            for(i=0;i<str.size();i++)
        {
            if(str[i]=='-')
            {
                if(i!=0)
                {
                    ans.push_back(str);
                    break;
                }
            }

            if(str[i]=='.')
            {
                j=i;
                flag++;
            }       
            if(!isdigit(str[i])&&str[i]!='.'&&str[i]!='-')   
            {                       // If it is a non numeric symbol other than the decimal point or minus sign 
                ans.push_back(str);
                break;
            }
        }

        if(i==str.size())
        {
            if(flag==0)
            {
                double dou=str_dou(str);
                if(dou>=-1000&&dou<=1000)
                {
                    ++count;
                    average+=dou;
                }
                else
                    ans.push_back(str);
            }
            else if(flag==1)
            {
                double dou=str_dou(str);
                if(i-j<=3)
                {
                    if(dou>=-1000&&dou<=1000)
                    {
                        ++count;
                        average+=dou;
                    }
                    else
                        ans.push_back(str);
                }
                else
                {
                    ans.push_back(str);

                }
            }
            else
            {
                ans.push_back(str);

            }
        }
    }
    for(int i=0;i<ans.size();++i)
    {
        printf("ERROR: %s is not a legal number\n",ans[i].c_str());
    }
    if(count==1)
        printf("The average of %d number is %.2f\n",count,average);
    else if(count>1)
        printf("The average of %d numbers is %.2f\n",count,average/count);
    else
        printf("The average of %d numbers is Undefined\n",count);
    return 0;
}


double str_dou(string s)
{
    double dou=0,pos=0.1;
    int flag=1,judge=1;
    for(auto a:s)
    {
        if(a=='-')
        {
            judge=-1;
            continue;
        }
        if(a=='.')
        {
            flag=0;
            continue;
        }
        if(flag)
            dou=dou*10+a-'0';
        else
        {
            dou+=(a-'0')*pos;
            pos*=0.1;
        }
    }
    dou*=judge;
    return dou;
}

This is a function that writes all the cases separately , How do you say , It feels better than the previous one .

#include <iostream>
#include <vector>
#include <string>
#include <cstdio>
using namespace std;
double str_dou(string s);
bool judge(string str);

int main()
{
    int n;
    cin >> n;
    string str;
    double average=0;
    int count=0;
    while(n--)
    {
        cin >> str;
        if(!judge(str))
            printf("ERROR: %s is not a legal number\n",str.c_str());
        else
        {
            average+=str_dou(str);
            ++count;
        }
    }
    if(count==1)
        printf("The average of %d number is %.2f\n",count,average);
    else if(count>1)
        printf("The average of %d numbers is %.2f\n",count,average/count);
    else
        printf("The average of %d numbers is Undefined\n",count);
    return 0;
}

double str_dou(string s)
{
    double dou=0,pos=0.1;
    int flag=1,judge=1;
    for(auto a:s)
    {
        if(a=='-')
        {
            judge=-1;
            continue;
        }
        if(a=='.')
        {
            flag=0;
            continue;
        }
        if(flag)
            dou=dou*10+a-'0';
        else
        {
            dou+=(a-'0')*pos;
            pos*=0.1;
        }
    }
    dou*=judge;
    return dou;
}

bool judge(string str)
{
    int i,j=0, flag=0;
    for(i=0;i<str.size();i++)
    {
        if(str[i]=='-')
        {
            if(i!=0)
                return false;
        }

        if(str[i]=='.')
        {
            j=i;
            flag++;
        }
        if(!isdigit(str[i])&&str[i]!='.'&&str[i]!='-')
                return false;
    }

    if(flag>1)
        return false;
    else if(flag==1)
    {
        if(i-j>3)
        return false;
        double dou=str_dou(str);
        if(dou<-1000||dou>1000)
            return false;
    }
    else
    {
        double dou=str_dou(str);
        if(dou<-1000||dou>1000)
            return false;
    }
    return true;
}

Finally, I read the code of Liu Shen , Write out the .

#include <cstdio>
#include <cctype>
#include <cstring>
#include <cmath>
using namespace std;
int main()
{
    int n;
    scanf("%d",&n);
    char s[50],ans[50];
    double db;
    int count=0;
    double average=0;
    while(n--)
    {
        cin >> s;
        sscanf(s,"%lf",&db);
        sprintf(ans,"%.2f",db);

        int len=strlen(s);
        int flag=0;
        for(int i=0;i<len;++i)
        {
            if(s[i]!=ans[i])
            {
                flag=1;
                break;
            }
        }
        if(flag==1||db>1000||db<-1000)
        {
            printf("ERROR: %s is not a legal number\n",s);
        }
        else
        {
            average+=db;
            ++count;
        }
    }
    if(count==1)
        printf("The average of %d number is %.2f\n",count,average);
    else if(count>1)
        printf("The average of %d numbers is %.2f\n",count,average/count);
    else
        printf("The average of %d numbers is Undefined\n",count);
    return 0;
}