c++ - 将输出定向到 C++ 中的 .txt 文件

Question

如何将此代码的输出定向到.txt文件中？

#include <iostream>
#include <vector>
#include <string>
#include <fstream>

using namespace std;

int main() {

    using std::cin;
    using std::cout;
    using std::endl;

    int input=1; 
    int sum=0; 
    int counter=1;

    while (input != 0) 
    {
        std::cout << "Please enter the hit data: "; 
        std::cin >> input; 

        if (input == 0) // after puting in data input zero 
        {
            break;
        }
        else if (input != 0)
        {
            sum += input; 
            counter++; 
        }
    }
    counter = counter - 1 ; 
    std::cout << "Sum of hits entered: " << sum << endl ; 
    std::cout << "Number of hits entered: " << counter << endl ;

    if ( counter < 100 ) 
    {
        std::cout << "The hits are less than 100" ;
    }
    else if ( counter > 100 ) 
    {
        std::cout << "The hits are greater than 100" ;
    }
    else if ( counter == 100 ) 
    {
        std::cout << "The hits are equal to 100" ;
    }
}

另外，我怎样才能让程序从另一个文件中读取数据，而不是用户输入数据.txt？我知道您可以在终端中轻松完成这一切；但是，我希望程序创建.txt文件。

另外，如何让程序识别某些数字？我希望它输出类似“有十二个数字 -11 计数”之类的东西。

标签： c++

Answer 1

用于std::ifstream从文件读取输入，并将std::ofstream输出写入文件。例如：

#include <iostream>
#include <fstream>

int main()
{
    int sum = 0; 
    int counter = 0;

    std::ifstream in("hits.txt");
    if (in.is_open())
    {
        while (in >> input)
        {
            sum += input; 
            ++counter;
        }
    }
    else
    {
        std::ofstream out("hits.txt");
        int input;

        do
        {
            std::cout << "Please enter the hit data: "; 

            // after putting in data, input zero 
            if (!(std::cin >> input) || (input == 0))
                break; 

            out << input << " ";

            sum += input; 
            ++counter;
        }
        while (true);
    }

    std::cout << "Sum of hits entered: " << sum << endl ; 
    std::cout << "Number of hits entered: " << counter << endl ;

    if (counter < 100)
    {
        std::cout << "The hits are less than 100" << std::endl;
    }
    else if (counter > 100) 
    {
        std::cout << "The hits are greater than 100" << std::endl;
    }
    else
    {
        std::cout << "The hits are equal to 100" << std::endl;
    }

    return 0;
}

另外，如何让程序识别某些数字？我希望它输出类似“有十二个数字 -11 计数”之类的东西。

您可以使用std:map它，例如：

#include <iostream>
#include <fstream>
#include <map>

int main()
{
    int sum = 0; 
    int counter = 0;
    std::map<int, int> hits; // hit counter

    std::ifstream in("hits.txt");
    if (in.is_open())
    {
        while (in >> input)
        {
            hits[input]++;
            sum += input; 
            ++counter;
        }
    }
    else
    {
        std::ofstream out("hits.txt");
        int input;

        do
        {
            std::cout << "Please enter the hit data: "; 

            // after putting in data, input zero 
            if (!(std::cin >> input) || (input == 0))
                break; 

            out << input << " ";

            hits[input]++;
            sum += input; 
            ++counter;
        }
        while (true);
    }

    std::cout << "Sum of hits entered: " << sum << endl ; 
    std::cout << "Number of hits entered: " << counter << endl ;

    if (counter < 100)
    {
        std::cout << "The hits are less than 100" << std::endl;
    }
    else if (counter > 100) 
    {
        std::cout << "The hits are greater than 100" << std::endl;
    }
    else
    {
        std::cout << "The hits are equal to 100" << std::endl;
    }

    for (auto &p : hits)
    {
        if (p.second == 1)
            std::cout << "there was 1 number " << p.first << " counted" << std:::endl;
        else
            std::cout << "there were " << p.second << " number " << p.first << "'s counted" << std:::endl;
    }

    /* or, if you are not using C++11 or later:

    for (std::map<int, int>::iterator iter = hits.begin(); iter != hits.end(); ++iter)
    {
        std::map<int, int>::value_type &p = *iter;

        if (p.second == 1)
            std::cout << "there was 1 number " << p.first << " counted" << std:::endl;
        else
            std::cout << "there were " << p.second << " number " << p.first << "'s counted" << std:::endl;
    }
    */

    return 0;
}