我如何得到十进制数的结果在除法？ C ++，Pi [英] How can I get the result with decimal number in division? C++, Pi

问题描述

我的学校给了我一个计算pi的任务。

My school give me an assignment to calculate pi.

结果应该是：

Question 4
Accuracy set at : 1000

term               pi
1                  4
100                3.13159
200                3.13659
300                3.13826
400                ...
...                ...

导致我的程序：

term               pi
1                  4
100                3
200                3
300                3
400                ...
...                ...

我猜，当我做（4 /分母），结果将丢失十进制数，虽然我已经改变了一些数据类型的声明从int到double。
（有些网站告诉我这样做）
也许我错了。

I guess that when I do (4 / denominator), the result will lose the decimal number although I have changed some declarations of data type from int to double. (Some websites tell me to do this.) Maybe I do it wrongly.

如何处理此问题？

以下是我的计划。

#include <iostream>
using namespace std;


class Four
{
private:
    int inputedAccuracy;
    double pi;
    int denominator;
    int doneTermCounter;
    double oneTerm;
    int negativeController;

public:
    double question4()
    {
        cout << "Accuracy set at : " ;
        cin >> inputedAccuracy;
        cout << endl;
        pi = 0.0;
        denominator = 1.0;
        doneTermCounter = 0;

        negativeController = 1;
        cout << "Term" << "            " << "pi" << endl;
        cout << "1  " << "             " << "4" << endl;


        for (inputedAccuracy; inputedAccuracy > 0; inputedAccuracy -= 100)
        {
            for (int doneTerm = 0; doneTerm < 100; doneTerm++)
            {
                pi = pi + (negativeController * 4 / denominator);
                negativeController *= -1;
                denominator += 2;
                doneTermCounter++;
            }
            if (doneTermCounter >= 10000)
                cout << doneTermCounter << "             " << pi << endl;
            else
                if (doneTermCounter >= 1000)
                    cout << doneTermCounter << "            " << pi << endl;
                else
                    cout << doneTermCounter << "             " << pi << endl;
        }
        return 0.0;
    }
};

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推荐答案

pi = pi + (negativeController * 4 / denominator);

（negativeController * 4 / denominator）表达式导致 int ，因为 negativeController 和分母 int 。换句话说，你在这里做一个整数除法，这解释了为什么你没有得到预期的结果。

The (negativeController * 4 / denominator) expression results in an int because both negativeController and denominator are int. In other words, you're doing an integer division here which explains why you don't get the expected result.

声明（或两者）为 double 强制执行浮点除法。

Declare either (or both) of them as double to force a floating-point division.

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