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为什么会输出NAN

未未来 发布于 2013-05-19 21:42， 4947 次点击
首先为上一帖的含糊不清道歉，

 主程序
程序代码：
#include<iostream>
#include<string>
#include<vector>
#include"Item_base.hpp"
#include"Bulk_item.hpp"
using namespace std;
int main(){
        vector<Item_base>itemvec;
        string isbn;
        double price,qty,discount;
        cout<<"Enter some Bulk_item objects"<<endl;
        while(cin>>isbn>>price>>qty>>discount){
                itemvec.push_back(Bulk_item(isbn,price,qty,discount));
        }
        
        double sum=0.0;
        for(vector<Item_base>::iterator iter=itemvec.begin();
        iter!=itemvec.end();++iter)
        sum+=iter->net_price(100);
        cout<<sum<<endl;
        return 0;
        
        
        
}

基类
程序代码：
class Item_base{
public:
Item_base(const std::string &book="",double sales_price=0.0):isbn(book),price(sales_price){
        
}

std::string book()const{
        return isbn;
}
virtual double net_price(std::size_t n)const {
        return n*price;
}
virtual ~Item_base(){
        
}


private:
std::string isbn;
protected:
double         price;


};
                                                                                 


继承类
程序代码：
class Bulk_item:public  Item_base{                                                         
                                                                                            
                                                                                            
                                                                                            
public :                                                                                    
                                                                                            
Bulk_item(const std::string &book="",double sales_price=0.0,size_t qty,double dis):         
Item_base(book,price),min_qty(qty),discount(dis){    }                                      
double net_price(std::size_t cnt)const{
        
        if(cnt>=min_qty)                                                                           
        return cnt*(1-discount)*price;                                                            
else                                                                                       
return cnt*price;                                                                           
}                                                               
private:                                                                                    
std::size_t min_qty;                                                                        
double discount;                                                                                   
};                                                                                          


当我一次输入  book 3 20 0.9
时，输出应该为 300 可是却输出NAN。 no a number ？？找不到错误在哪。

虽然这个原理知识都懂了，但是得不到想要的结果总是难受的，请前辈们指教。
3 回复
#2
rjsp2013-05-20 08:26
Bulk_item(const std::string &book="",double sales_price=0.0,size_t qty,double dis)
--------- 我想世上没有哪个编译器能让这垃圾可以编译通过，不知道楼主是怎么能运行它的？
#3
未未来2013-05-20 10:04
回复 2楼 rjsp
他可以运行呀，，我是照书上习题打的><
#4
rjsp2013-05-20 14:56
你的代码中有无数莫名其妙的地方，不知道是用于测试还是……，反正我全一股脑改掉了
以下修改后的代码虽然不是C++风格，但没啥语法错误。输入 book 3 20 0.9 输出 30
程序代码：
#include <string>

class Item_base
{
public:
    Item_base( const std::string& book="", double sales_price=0.0 ) : isbn(book), price(sales_price)
    {
    }

    std::string book() const
    {
        return isbn;
    }
    virtual double net_price( size_t cnt ) const
    {
        return cnt*price;
    }
    virtual ~Item_base()
    {
    }

private:
    std::string isbn;
protected:
    double price;
};

class Bulk_item : public Item_base
{
public:
    Bulk_item( const std::string& book="", double sales_price=0.0, size_t qty=0, double dis=0.0 ) : Item_base(book,sales_price), min_qty(qty), discount(dis)
    {
    }
    virtual double net_price( size_t cnt ) const
    {
        if( cnt >= min_qty )
            return cnt*(1-discount)*price;
        else
            return cnt*price;
    }
private:
    size_t min_qty;
    double discount;
};

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<Bulk_item> itemvec;
    {
        cout << "Enter some Bulk_item objects" << endl;
        string isbn;
        double price;
        size_t qty;
        double discount;
        while( cin>>isbn>>price>>qty>>discount )
        {
            itemvec.push_back( Bulk_item(isbn,price,qty,discount) );
        }
    }

    double sum=0.0;
    for( vector<Bulk_item>::const_iterator itor=itemvec.begin(); itor!=itemvec.end(); ++itor )
        sum += itor->net_price( 100 );
    cout << sum << endl;

    return 0;
}
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