c++ - 数学计算和 setprecision() 函数有问题

Question

我似乎遇到了 C++ 编码问题。它涉及数学运算，我似乎让我的所有输出都正确，除了最后一个。除此之外，我的答案的小数点格式似乎不正确。答案应该包含两位小数，但我的四个小数点答案中只有两个似乎有两位小数。当我尝试使用 precision() 函数时，答案变成了我不想要的科学记数法。

这里是问答:

这是我的代码:

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{
    float principal;
    float interest_rate;
    float times_compounded;

    cout << "Hello, please enter a value for your principal: ";
    cin >> principal;
    cout << principal << endl;
    cout << "Please enter a value for your interest rate: ";
    cin >> interest_rate;
    cout << interest_rate << "%" << endl;
    cout << "Please enter the number of times the interest is compounded during the year: ";
    cin >> times_compounded;
    cout << times_compounded << endl << endl;

    float interest = interest_rate * 10.197647;
    float amount = principal * pow((1 + (interest_rate/times_compounded)), times_compounded);

    cout << "Interest Rate: " << setw(19) << interest_rate << "%" << endl;
    cout << "Times Compounded: " << setw(17) << times_compounded << endl;
    cout << "Principal: " << setw(17) << "$ " << setw(7) << principal << endl;
    cout << "Interest: " << setw(20) << "$ " << interest << endl;
    cout << "Amount in Savings: " << setw(9) << "$ " << amount;

    return 0;
}

这是我的三个输入:1000, 4.25, 12

如有任何反馈，我们将不胜感激，感谢您抽出宝贵时间。

Answer 1

首先，最后一个值是错误的，因为您在公式中将利率用作正常数字，尽管它实际上是一个百分比。所以你需要将它除以 100:

float amount = principal * pow((1 + ((interest_rate / 100) /times_compounded)), times_compounded);

现在对于精度，您可以结合使用 std::fixed 和 std::setprecision 来设置使用 std 时的默认浮点打印精度::cout。我们可以使用宏使其更具可读性，例如:

#define FIXED_FLOAT(x, p) std::fixed<<std::setprecision(p)<<(x)

因此，完整的输出部分如下所示:

cout << "Interest Rate: " << setw(19) << FIXED_FLOAT(interest_rate, 2) << "%" << endl;
cout << "Times Compounded: " << setw(17) << FIXED_FLOAT(times_compounded, 0) << endl;
cout << "Principal: " << setw(17) << "$ " << setw(7) << FIXED_FLOAT(principal, 2) << endl;
cout << "Interest: " << setw(20) << "$ " << FIXED_FLOAT(interest, 2) << endl;
cout << "Amount in Savings: " << setw(9) << "$ " << FIXED_FLOAT(amount, 2);

此外，interest = interest_rate * 10.197647 似乎有问题。利息应该只是减去本金的金额。