c++ - 如何在C++中输出一个数字乘以另一个变量的值的双精度值? [英] How to output a double that is the value of a number multiplied by another variable in C++?

问题描述

我正在尝试使用 double 为我的 weight_Fee 获取输出，但我似乎无法获得正确的值.我曾尝试使用 float，但我也无法让它工作.

I'm trying to get an output for my weight_Fee using double, and I cannot seem to get the correct value. I have tried using float, but I haven't been able to get that to work either.

我的目标是获得一个包含两位小数的输出值，就像我要计算成本一样，但我每次都得到 0.00.

My goal is to get an output value containing two decimal places as if I were to be calculating a cost, but I get 0.00 every time.

我是 C++ 的新手，所以如果有人能告诉我我做错了什么，那将是一个很大的帮助.谢谢.

I'm new to C++, so if anyone can tell me what I'm doing wrong, it would be a big help. Thanks.

#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <ctime>
using namespace std;

int main() {

double animal_Weight;   
double weight_Fee = .5 * animal_Weight;

cout << "In rounded poundage, how much does your animal weigh? ";
cin >> animal_Weight;

cout << setprecision (2) << fixed << weight_Fee;

return 0;
}

推荐答案

double weight_Fee = 0.5 * animal_Weight;

当您像这样初始化 weight_Fee 时，您将其设置为等于 0.5 *animal_Weight 的当前值.由于这是当前未定义的 weight_Fee 将是一些垃圾值.

When you initialize weight_Fee like that you are setting it equal to 0.5 * the current value of animal_Weight. Since this is currently undefined weight_Fee will be some garbage value.

当您稍后根据用户输入将 animal_Weight 设置为某些内容时，不会更改先前变量的值.您必须再次使用该语句来设置 weight_Fee = 0.5 * animal_Weight

When you set animal_Weight to something based on user input later on, that won't change the value of a previous variable. You'll have to use that statement again to set weight_Fee = 0.5 * the current value of animal_Weight

最好的做法可能是在顶部声明 weight_Fee，并且在您将 animal_Weight 设置为您想要的值之前不要定义它.

The best thing to do is probably to just declare weight_Fee at the top, and not define it until you have set animal_Weight to what you want it to be.

像这样:

#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <ctime>
using namespace std;

int main() {

    double animal_Weight;   
    double weight_Fee;

    cout << "In rounded poundage, how much does your animal weigh? ";
    cin >> animal_Weight;

    weight_Fee = .5 * animal_Weight

    cout << setprecision (2) << fixed << weight_Fee;

    return 0;
}

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