我正在为我的编程课做作业。我对发生的事感到困惑。我的代码编译没有问题，但是当我运行它时，它没有做任何事情。我决定进入几次，仍然没有。然后我输入“1”并按Enter键，四次之后，最终显示程序运行时应该显示的菜单。任何人都可以帮我发现这个错误吗？
部首：
/*
+-----------------------------------+
| Fruit |
+-----------------------------------+
| -fruitName : String |
| -priceOfFruit : Double |
| -numberOfFruit : Integer |
| -numberSold : Integer |
+-----------------------------------+
| <<constructor>> |
| Fruit(name: String |
| price: Double |
| num : Integer) |
| <<constructor>> |
| Fruit(name: String) |
| <<constructor>> |
| Fruit() |
| +setFruitName(name : String) |
| +setPriceOfFruit(price : Double) |
| +setNumberOfFruit(num : Integer) |
| +setNumberSold(num : Integer) |
| +getFruitName() : String |
| +getPriceOfFruit() : Double |
| +getNumberOfFruit() : Integer |
| +getNumberSold() : Integer |
| +amountSold() : Double |
| +buy() : Boolean |
+-----------------------------------+
*/
#include <string>
using namespace std;
#ifndef FRUIT_H
#define FRUIT_H
class Fruit
{
private:
string fruitName;
double priceOfFruit;
int numberOfFruit;
int numberSold;
public:
Fruit(string name, double price, int num);
Fruit(string name);
Fruit();
void setFruitName(string name);
void setPriceOfFruit(double price);
void setNumberOfFruit(int num);
void setNumberSold(int num);
string getFruitName();
double getPriceOfFruit();
int getNumberOfFruit();
int getNumberSold();
double amountSold();
bool buy();
};
#endif
实现：
#include <iostream>
#include <iomanip>
#include <string>
#include "Fruit.h"
using namespace std;
Fruit::Fruit(string name, double price, int num)
{
fruitName = name;
priceOfFruit = price;
numberOfFruit = num;
numberSold = 0;
}
Fruit::Fruit(string name)
{
fruitName = name;
priceOfFruit = 0;
numberOfFruit = 0;
numberSold = 0;
}
Fruit::Fruit()
{
fruitName = "";
priceOfFruit = 0;
numberOfFruit = 0;
numberSold = 0;
}
void Fruit::setFruitName(string name)
{
fruitName = name;
}
void Fruit::setPriceOfFruit(double price)
{
if (price >= 0)
priceOfFruit = price;
else
while (price < 0)
cout << "\nThe price cannot be negative. Please try again: " << endl;
cin >> price;
if (price >= 0)
priceOfFruit = price;
}
void Fruit::setNumberOfFruit(int num)
{
if (num >= 0)
numberOfFruit = num;
else
while (num < 0)
cout << "\nThe number of fruit cannot be negative. Please try again: " << endl;
cin >> num;
if (num >= 0)
numberOfFruit = num;
}
string Fruit::getFruitName()
{
return fruitName;
}
double Fruit::getPriceOfFruit()
{
return priceOfFruit;
}
int Fruit::getNumberOfFruit()
{
return numberOfFruit;
}
int Fruit::getNumberSold()
{
return numberSold;
}
double Fruit::amountSold()
{
return numberSold * priceOfFruit;
}
bool Fruit::buy()
{
bool transaction;
int buying, available = 0;
numberOfFruit = available;
cout << "\n" << fruitName << " .......... " << "$"
<< setfill('0') << setw(4) << priceOfFruit
<< "\nPlease enter the number of "<< fruitName
<< "s to purchase: " << endl;
cin >> buying;
if (buying > available) {
transaction = false;
return transaction;
}
else {
numberOfFruit = available - buying;
numberSold = buying;
transaction = true;
return transaction;
}
}
主：
#include <iostream>
#include <iomanip>
#include <string>
#include "Fruit.h"
using namespace std;
int main()
{
int selection = 5;
bool transaction;
double total;
Fruit apple("Apple", 1.99, 10);
Fruit banana("Banana");
Fruit orange;
banana.setPriceOfFruit(0.79);
banana.setNumberOfFruit(8);
orange.setFruitName("Orange");
orange.setPriceOfFruit(1.49);
orange.setNumberOfFruit(7);
do {
cout << " Fruit Stand "
<< "\n---------------"
<< "\n1. Buy Apple"
<< "\n2. Buy Banana"
<< "\n3. Buy Orange"
<< "\n4. Print Total"
<< "\n0. Quit"
<< "\nPlease make a selection: " << endl;
cin >> selection;
while (selection < 0 && selection > 4) {
cout << "\nSorry, that was an invalid selection."
<< "Please try again: " << endl;
cin >> selection;
}
if (selection == 1)
transaction = apple.buy();
else if (selection == 2)
transaction = banana.buy();
else if (selection == 3)
transaction = orange.buy();
else if (selection == 4)
cout << "Your current total is $" << setfill('0') << setw(4) << total << endl;
else
cout << "\nThank you for shopping at the Fruit Stand!" << endl;
if (transaction == true) {
cout << "\nThank you for your purchase!\n" << endl;
total = apple.amountSold() + banana.amountSold() + orange.amountSold();
}
else
cout << "\nSorry, out of stock.\n" << endl;
} while (selection != 0);
system("pause");
return 0;
}
答案 0 :(得分：1)
这不符合您的期望：
void Fruit::setNumberOfFruit(int num)
{
if (num >= 0)
numberOfFruit = num;
else
while (num < 0)
cout << "\nThe number of fruit cannot be negative. Please try again: " << endl;
cin >> num;
if (num >= 0)
numberOfFruit = num;
}
请使用大括号 - 这是C ++，而不是python。就像现在一样，代码相当于：
void Fruit::setNumberOfFruit(int num)
{
if (num >= 0)
numberOfFruit = num;
else
while (num < 0)
cout << "\nThe number of fruit cannot be negative. Please try again: " << endl;
cin >> num;
if (num >= 0)
numberOfFruit = num;
}
这意味着当您在setNumberOfFruit()中致电main()时，总是尝试从stdin读取一个号码。将其更改为：
void Fruit::setNumberOfFruit(int num)
{
if (num >= 0)
numberOfFruit = num;
else {
while (num < 0) {
cout << "\nThe number of fruit cannot be negative. Please try again: " << endl;
cin >> num;
if (num >= 0)
numberOfFruit = num;
}
}
}
事实上，也许更好的选择是做到这一点：
void Fruit::setNumberOfFruit(int num)
{
while (num < 0) {
cout << "\nThe number of fruit cannot be negative. Please try again: " << endl;
cin >> num;
}
numberOfFruit = num;
}
或者，更好的是，如果num不在您期望的范围内，则抛出异常，并在main()或调用setter的任何地方处理该异常 - 在我看来，它不是很好的设计可以做你在setter方法中做的那些事情。