从文本文件中读取 100 个数字并找到最小值和最大值

Question

Created a text file and put in 100 random numbers. Trying to read the file. The text file looks like:

 27 12 37 53 83 2

    #include<iostream>
    #include<fstream>

    using namespace std;

    int main()
    {
       int i,min,max;
       ifstream fin;
       fin.open("DATA.txt",ios::in);
       fin>>i;
       max=i;
       min=i;

       while(fin>>i)
       {
           if(i>max)
               max=i;
           if(i<min)
               min=i;
       }
       cout<<max<<" "<<min;
       fin.close();
   }

I originally tried to do it using read function but it gives garbage values. Why does this code not work?

    #include<iostream>
    #include<fstream>

    using namespace std;

    int main()
    {
       int i,min,max;
       ifstream fin;
       fin.open("DATA.txt",ios::in);
       fin.read((char*)&i,sizeof(i));
       max=i;
       min=i;
       while(fin)
       {
           fin.read((char*)&i,sizeof(i));
           if(i>max)
               max=i;
           if(i<min)
               min=i;
       }
       cout<<max<<" "<<min;
       fin.close();
   }

Answer 1

You can do the following:

    #include<iostream>
    #include<fstream>

    using namespace std;

    int main()
    {
       int i,min,max;
       ifstream fin;
       fin.open("DATA.txt",ios::in);
       max=INT_MIN; // least possible int value
       min=INT_MAX; // largest possible int value

       while(fin>>i)// reads till the end of file
       {
           if(i>max)
               max=i;
           if(i<min)
               min=i;
       }
       cout<<max<<" "<<min;
       fin.close();
   }

Answer 2

Assuming sizeof(int) == 4 (which is true on most platforms), the first time you execute the line

fin.read((char*)&i,sizeof(i));

it will read the first 4 bytes (=characters) of the file, which are "27 1" . Assuming the file is ASCII encoded, these 4 bytes have the following values:

1. 50 ( ASCII code for the digit '2' )
2. 55 (ASCII code for the digit '7' )
3. 32 (ASCII code for the character ' ' )
4. 49 (ASCII code for the digit '1' )

Assuming that you are on a little-endian platform, the mentioned byte values will result in an int with the value 824,194,866 .

This is what happens when you read your text file as binary data, which is obviously not what you want. What you want is to read the file as text. You want to read digits until you encounter a non-digit character, interpret these digits as a number, and then write that number to an int variable. This is exactly what the << stream extraction operator does in the expression fin>>i that you are using.

Therefore, your second piece of code is fundamentally incorrect, because it interprets the file data as binary, whereas your first piece of code is fundamentally correct, as it interprets the file data as text.

Answer 3

The question is already answered. However, we should not go without an additional solution that shows the "more modern" C++ approach.

And therefore I offer the below answer for your kind evaluation.

#include <iostream>
#include <fstream>
#include <algorithm>
#include <iterator>

int main() {
    // Open file and check, if it could be opened. (using C++17 features)
    if (std::ifstream dataFileStream{ "data.txt" }; dataFileStream) {

        // Read all values and get iterator to min and max element
        const auto [min, max] = std::minmax_element(std::istream_iterator<int>(dataFileStream), {});
        
        // Show result to user
        std::cout << "Min: " << *min << " \t Max: " << *max << '\n';
    }
    else {
        // File could not be opened. Show error
        std::cerr << "\nError: Could not open source file\n\n";
    }
    return 0;
}

This is a short and compact solution. Without any loop.

Maybe somebody will be inspired by it.

Answer 4

All answers are given. Your part one is totally fine and the reason for the problem with part 2 has been explained very could by Andreas Wenzel +1.

Last but not least I will show an (one of many possible) additional solution, using more modern C++ elements.

#include <iostream>
#include <fstream>
#include <algorithm>
#include <iterator>

int main() {
    // Open file and check, if it could be opened
    if (std::ifstream dataFileStream{ "data.txt" }; dataFileStream) {

        // Read all values and get iterator to min and max element
        const auto [min, max] = std::minmax_element(std::istream_iterator<int>(dataFileStream), {});
        
        // Show result to user
        std::cout << "Min: " << *min << " \t Max: " << *max << '\n';
    }
    else {
        // File could not be opened. Show error
        std::cerr << "\nError: Could not open source file\n\n";
    }
    return 0;
}