Question

这是我编写的程序。由于某种原因，它将最后一个元素值填充到数组的所有元素中。该程序应该只是打开并读取文件。对行求和。对列求和，然后对所有元素求和。

#include <iostream>
#include <iomanip>
#include <fstream>
using namespace std;
const int NUM_TYPE = 5; // num of types of salsa
const int NUM_SALE = 4; // num of quarters per salsa

void salsaIn(float salsa[][NUM_SALE]);
void salsaType(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE);
void salsaQ(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE);
void totalSalsa(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE);
void displayArray(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE);

int main()
{
    float salsa[NUM_TYPE][NUM_SALE];

    salsaIn(salsa);
    displayArray(salsa, NUM_TYPE, NUM_SALE);
    salsaType(salsa, NUM_TYPE, NUM_SALE);
    salsaQ(salsa, NUM_TYPE, NUM_SALE);
    totalSalsa(salsa, NUM_TYPE, NUM_SALE);

    return 0;
}
//reads the salsa.txt file
void salsaIn(float salsa[][NUM_SALE])
{
    float salsaT = 0;
    ifstream file("salsa.txt");

    if (file.is_open())
    {
        cout << "Successful. Reading data." << endl;
        while (!file.eof())
        {
            for (int i = 0; i < NUM_TYPE; i++)
            {
                for (int j = 0; j < NUM_SALE; j++)
                {

                    file >> salsaT;
                    if (salsa < 0)
                    {
                        cout << "error, value less than 0, set to 0"<<endl;
                        salsaT = 0;
                    }

                    salsa[i][j] = salsaT;
                }
            }
        }

    }
    file.close();

    return;
}
//calculates and displays sales for each salsa type
void salsaType(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE)
{
    for (int row = 0; row < NUM_TYPE; row++)
    {
        float total = 0;

        for (int col = 0; col < NUM_SALE; col++)
        {
            total += salsa[row][col];
        }
        //display the total sales for each salsa type.
        cout << "total sales for salsa " << (row + 1) << " is " << total
                << endl;

        return;
    }

}
void displayArray(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE)
{
    for (int row = 0; row < NUM_TYPE; row++)
    {
        float total = 0;

        for (int col = 0; col < NUM_SALE; col++)
        {
            cout << setw(5) << salsa[row][col] << endl;
        }
        //display the total sales for each salsa type.
    }

    return;
}
//calculates and displays the sales of each quarter.
void salsaQ(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE)
{
    for (int col = 0; col < NUM_SALE; col++)
    {
        float totalq = 0;

        for (int row = 0; row < NUM_TYPE; row++)
            totalq += salsa[row][col];

        cout << "Sales for quarter " << (col + 1) << " is " << totalq << endl;
    }

    return;

}
//calculates and displays the sales for the company last year.
void totalSalsa(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE)
{
    float totalS = 0;
    for (int row = 0; row < NUM_TYPE; row++)
    {

        for (int col = 0; col < NUM_SALE; col++)

            totalS += salsa[row][col];

    }

    cout << "The total sales for the company last year is " << totalS << endl;
}

这是程序的最终输出。

Successful. Reading data.
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
3905.64
total sales for salsa 1 is 15622.6
Sales for quarter 1 is 19528.2
Sales for quarter 2 is 19528.2
Sales for quarter 3 is 19528.2
Sales for quarter 4 is 19528.2
The total sales for the company last year is 78112.8

感谢帮助人员。我有点困在程序的其余部分。

Answer 1

发生了什么事

while (!file.eof())

循环直到设置EOF标志。除非程序尝试从文件中读取值并找到文件的末尾，否则将不会设置此标志。通常，这意味着在程序尝试从文件中读取值并失败之前，因为没有更多的值可读取，因此EOF标志不会被设置。

{
    for (int i = 0; i < NUM_TYPE; i++)
    {
        for (int j = 0; j < NUM_SALE; j++)
        {

这些循环将尝试从文件中读取20个值

            file >> salsaT;

从文件中读取一个值。没有检查以确保从文件中读取了一个值。如果失败，则C ++ 11之前的salsaT中的值不变。在C ++ 11之后，它被清零。如果您不使用C ++ 11进行编译，那么您会重复输入最后一个数字。

            if (salsa < 0) // unrelated bug here
            {
                cout << "error, value less than 0, set to 0"<<endl;
                salsaT = 0;
            }

            salsa[i][j] = salsaT;
        }
    }
}

从文件或while (!file.eof())循环的每次迭代中读取

20个值。如果文件中恰好有20个值，则全部读取20个值。可能未设置EOF，因此进入了while循环。另外20个值被读入同一数组，但是这次没有任何值可读取。数组很可能包含成功读取的最后一个值的20个重复。

解决方案：

while循环之死！

for (int i = 0; i < NUM_TYPE; i++)
{
    for (int j = 0; j < NUM_SALE; j++)
    { // read 20 values from file
        if (file >> salsaT)
        { // if we got a value
            if (salsaT < 0)
            {
                cout << "error, value less than 0, set to 0"<<endl;
                salsaT = 0;
            }
        }
        else
        { // Bad or no value. try to clean up.
            if (file.eof())
            {
                cout << "File ended too soon"<<endl;
            }
            else
            {
                cout << "error, bad value in file"<<endl;
                file.clear();
                file.ignore(numeric_limits<streamsize>::max(), '\n');
            }
            salsaT = 0;
        }
        salsa[i][j] = salsaT; // store
    }
}

C ++ 2d数组用文件中的最后一个元素值填充所有元素

1 个答案: