Question

我遇到以下代码行的问题：

double answer;
answer = num[count] / den[count]
cout << " Fraction" << count + 1 << " " << num[count] 
     << " / " << den[count] << " = " << answer << endl;

为什么我的回答不起作用？我忽略了什么吗？我正在使用数组，并从单独的文本文件中获取数据。当我使用上面的代码时，我得到了正确划分的数字，但答案是不正确的。它通常是0或1的随机数。

这是我的代码：

#include <iostream>
#include <fstream>
#include <iomanip>
#include <cstdlib>

using namespace std;
void read_data(int num[], int den[], int size);
void showValues(int num[],int den[], int size);

int main()
{
    const int size1 = 12;
    const int size2 = 12;
    ifstream dataIn;
    int num[12];
    int den[12];

    read_data(num,den,size1);
    cout << "Here are the fractions: " << endl;
    showValues(num,den,size1);

    system("PAUSE");
    return 0;
}

void read_data(int num[], int den[], int size)
{
    ifstream dataIn;
    dataIn.open("walrus.txt");

    if( dataIn.fail() )
         {
        cout << "File does not exist." << endl;
        exit(1);
         }

     int count;
     for ( count = 0; count < size; count++ )
     {
         dataIn >> num[count];
     }

     for (count = 0; count < size; count++)
     {
         dataIn >> den[count];
     }


     dataIn.close();
 }

void showValues(int num[],int den[], int size)
{
    int count;
        for (count = 0; count < size; count++)
        {
            if (den[count] == 0)
            {
                 cout << " Fraction" << count + 1 << " " 
                      << num[count] << " /" << den[count] 
                      << " Is invalid" << endl;
             }
            else
            {
                double answer;
                answer = num[count] / den[count];
             cout << " Fraction" << count + 1 << " " 
                  << num[count] << " / " << den[count] 
                  << " = " << answer << endl;
             }
        }
 }

Answer 1

@main ifstream dataIn; 您没有使用此对象

@function read_data：

 int count;
 for ( count = 0; count < size; count++ )
 {
     dataIn >> num[count];
 }

 for (count = 0; count < size; count++)
 {
     dataIn >> den[count];
 }

假设你的文件看起来像：

1 2 23 32 44 // numerators
2 3 1 99 24 // den

正确的阅读方式是：

int count = 0;
while( count < size && dataIn >> num[count++] ) // numerators
    ;

count = 0;
while( count < size && dataIn >> den[count++] )
    ;

@function showValues：尝试改变

   double answer;
    answer = num[count] / den[count];
 cout << " Fraction" << count + 1 << " " 
      << num[count] << " / " << den[count] 
      << " = " << answer << endl;

到：

double answer = static_cast<double>(num[count]) / den[count];
cout << " Fraction" << count + 1 << " " 
     << num[count] << " / " << den[count] << " = " << answer << endl;

Answer 2

在C和C ++中，如果你这样做，

double answer = 10 / 3;

你的回答是3.原因是你有2个整数并且会发生整数除法。然后，结果输出被隐式转换为double。所以步骤是，

double answer = 10/3
double answer = 3
double answer = 3.0

要解决此问题，请告诉编译器您希望将其视为浮点除法。

double answer = 10.0 / 3;

这适用于，

double answer = 10.0 / 3
double answer = 10.0 / 3.0
double answer = 3.33333333 ...

编译器将隐式地将3转换为更大的double类型3.0。

因此，在您的代码中，您必须通过将至少一个除法参数转换为double来将整数除法转换为浮点除法。

double foo = num[count] / den[count];

简单地变成

double foo = num[count] / static_cast<double>(den[count]);

或者，如果一个或两个数组都是double类型，那么你就不会遇到需要强制转换的问题。

分部答案没有正确执行

2 个答案: