为什么我的输出总是0.00？

// The output for cubic yards is always 0.00 

#include <iostream> 
using namespace std; 

class Road 
{ 
public: 
    void set_road_width(double width); 
    void set_road_length(double length); 
    void set_road_depth(double depth); 
    double asphalt_required(); 
private: 
    double roadDepth; 
    double roadWidth; 
    double roadLength; 
    double roadAsphalt; 
}; 

int main() 
{ 
    Road width, length, depth, asphalt, output; 
    double inputWidth = 0.0, inputLength = 0.0, inputDepth = 0.0; 


    cout << "Enter the width of the road in miles: "; 
    cin >> inputWidth; 
    cout << endl; 
    cout << "Enter the length of the road in miles: "; 
    cin >> inputLength; 
    cout << endl; 
    cout << "Enter the depth of the road in inches: "; 
    cin >> inputDepth; 
    cout << endl; 


    width.set_road_width(inputWidth); 
    length.set_road_length(inputLength); 
    depth.set_road_depth(inputDepth); 
    asphalt.asphalt_required(); 


    cout.setf(ios::fixed); 
    cout.setf(ios::showpoint); 
    cout.precision(2); 


    cout << "The width of the road is: " << inputWidth << " mile(s)" << endl; 
    cout << "The length of the road is: " << inputLength << " mile(s)" << endl; 
    cout << "The depth of the road is: " << inputDepth << " inch(es)" << endl; 
    cout << "Asphalt required: " << output.asphalt_required() << " cubic yard(s)" << endl; 

    return 0; 
} 

void Road::set_road_width(double width) 
{ 
    roadWidth = width; 
} 

void Road::set_road_length(double length) 
{ 
    roadLength = length; 
} 

void Road::set_road_depth(double depth) 
{ 
    roadDepth = depth; 
} 

double Road::asphalt_required() 
{ 
    double widthIntoYards = 0.0, lengthIntoYards = 0.0, depthIntoYards = 0.0, yardConversionFactor = 0.333; 

    widthIntoYards = ((roadWidth * 5280.00) * yardConversionFactor); 
    lengthIntoYards = ((roadLength * 5280.00) * yardConversionFactor); 
    depthIntoYards = ((roadDepth/12.00) * yardConversionFactor); 

    roadAsphalt = (widthIntoYards * lengthIntoYards * depthIntoYards); 

    return(roadAsphalt); 
}

输出始终为0.00。我认为它与asphalt_required（）函数或与线cout < <“沥青需要：”< < output.asphalt_required（）< <“cubic yard（s）”< < endl;现在我只写了，因为Stack Overflow说我需要添加更多的上下文，也许是为了平衡代码。为什么我的输出总是0.00？

来源

2015-02-06 Tapan

'道路宽度，长度，深度，沥青，输出;'这对我没有意义。你有5条道路叫做“宽度”，“长度”，“深度”，“沥青”和“输出”？我假设你只想拥有一条具有不同属性的道路。 – Matthew 2015-02-06 05:24:57

输出始终为'0.0'，因为您已将其分配给该值，并且不会在任何地方更改。您应该使用调试器查看执行情况，并且您会看到问题。 – 2015-02-06 05:27:49

我修好了Road类。我做了一个道路对象，道路，它工作。感谢所有的答复。 – Tapan 2015-02-06 07:56:52

你只需要一个单一的road：

int main() 
{ 
    Road road; 
    double inputWidth = 0.0, inputLength = 0.0, inputDepth = 0.0; 


    cout << "Enter the width of the road in miles: "; 
    cin >> inputWidth; 
    cout << endl; 
    cout << "Enter the length of the road in miles: "; 
    cin >> inputLength; 
    cout << endl; 
    cout << "Enter the depth of the road in inches: "; 
    cin >> inputDepth; 
    cout << endl; 


    road.set_road_width(inputWidth); 
    road.set_road_length(inputLength); 
    road.set_road_depth(inputDepth); 
    road.asphalt_required(); 


    cout.setf(ios::fixed); 
    cout.setf(ios::showpoint); 
    cout.precision(2); 


    cout << "The width of the road is: " << inputWidth << " mile(s)" << endl; 
    cout << "The length of the road is: " << inputLength << " mile(s)" << endl; 
    cout << "The depth of the road is: " << inputDepth << " inch(es)" << endl; 
    cout << "Asphalt required: " << road.asphalt_required() << " cubic yard(s)" << endl; 

    return 0; 
}

来源

2015-02-06 05:28:34 tofi9

除了构建它并打印其asphalt_required()以外，您绝不会对output做任何事情。这就是为什么它打印零：你从来没有以任何方式实际修改output！

除此之外，您可能想要考虑为什么要构建如此多的Road实例。似乎应该只有一个。现在，您有五个Road s：三个是一维的，两个是零维的。

来源

2015-02-06 05:27:14

看来，问题就在这里：

Road width, length, depth, asphalt, output; 

/// Some code 

width.set_road_width(inputWidth); 
length.set_road_length(inputLength); 
depth.set_road_depth(inputDepth); 
asphalt.asphalt_required();

，它怎么可能

Road output; 

/// Some code 

output.set_road_width(inputWidth); 
output.set_road_length(inputLength); 
output.set_road_depth(inputDepth); 
output.asphalt_required();

这将帮助你。

这是因为您创建了一个类的实例，您已经拥有了计算的所有内容。在这种情况下，可能是更好的，有你在你的构造函数需要的一切，就像这样：

class Road 
{ 
public: 
    Road(double width, double length, double depth) 
    double asphalt_required(); 
private: 
    double roadDepth; 
    double roadWidth; 
    double roadLength; 
    double roadAsphalt; 
}; 

Road::Road(double width, double length, double depth) 
: roadDepth(depth) 
, roadWidth(width) 
, roadLength(length) { 
} 

/// Other code...

这是更好，因为它也可能阻止您这样的错误。你需要做的一切是做一些修改

double inputWidth = 0.0, inputLength = 0.0, inputDepth = 0.0; 

/// Here we got all needed values... 

Road output(inputWidth, inputLength, inputDepth); 
output.asphalt_required(); 

/// And then output...

来源

2015-02-06 05:29:49

为什么我的输出总是0.00？

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