“
定义一个如下所示的CNumber类，并以其为基类派生出素数类CPrimeNumber，完全平方数类CCompleteSquareNumber和回文数类CPalindromeNumber。
class CNumber
{
protected:
char *p_type; // points to the text stating type of the number
public:
CNumber(char *p_number_type);
void print() { }
void printYes() { cout < < "It is a " < < p_type < < endl; }
void printNo() { cout < < "It is not a " < < p_type < < endl; }
virtual ~CNumber() { delete [] p_type; }
};
class CPrimeNumber : public CNumber
{
protected:
long n;
public:
CPrimeNumber(long n_val);
void print();
~CPrimeNumber() { }
};
class CCompleteSquareNumber : public CNumber
{
protected:
long n;
public:
CCompleteSquareNumber(long n_val);
void print();
~CCompleteSquareNumber() { }
};
class CPalindromeNumber : public CNumber
{
protected:
long n;
public:
CPalindromeNumber(long n_val)
void print();
~CPalindromeNumber() { }
};
void CPalindromeNumber::print()
{
long n1, sum=0;
int t;
n1 = n*n;
while (n1 != 0)
{
t = n1%10;
sum = sum*10 + t;
n1 = n1/10;
}
if (sum == n*n)
printYes();
else
printNo();
}
为了能实现如下例图所示的输出结果，应该怎样编写各个类其余各成员函数，并完成主函数的实现。
Enter a number <0 to exit>:13
Enter the type of number you want to check:
1.Prime number
2.Complete aquare number
3.Palindrome number
1
It is a Prime number
Enter a number <0 to exit>:16
Enter the type of number you want to check:
1.Prime number
2.Complete aquare number
3.Palindrome number
2
It is a Complete aquare number
Enter a number <0 to exit>:11
Enter the type of number you want to check:
1.Prime number
2.Complete aquare number
3.Palindrome number
3
It is a Palindrome number
Enter a number <0 to exit>:0
Press any key to continue
”
= = = = = = = = = = = = = = = = = = = = = = = = = = = = =
上文为网友的提问，其中“aquare”疑为“Square”之笔误。
这位朋友给出的部分实现代码，很是值得商榷，比如在类Cnumber中：
1. char *p_type;根本没有必要；
2. 下面3个函数如果都需要的话，将其设为虚函数更为恰当。
void print() { }
void printYes() { cout < < "It is a " < < p_type < < endl; }
void printNo() { cout < < "It is not a " < < p_type < < endl; }
还有，根据一般的规则，如果在类的定义出实现相关函数，最好使用如下的方式：
inline void printYes() { cout < < "It is a " < < p_type < < endl; }
…等等。
这个问题的实现完全可以不用所谓的设计模式，在下面的代码中，纯粹是为了顺便说明Factory Method这个设计模式的用法而引入了Factory Method模式，在这里，使用设计模式会增加很多代码。但这并不是说，设计模式不重要，事实上，设计模式是非常重要的。
代码如下：
// 抽象基类CNnumber
#include <math.h>
#include <iostream>
using namespace std;
class CNumber
{
public:
CNumber();
virtual void print() = 0; // 纯虚函数
virtual ~CNumber();
};
// 基类CNnumber的实现
CNumber::CNumber()
{
}
CNumber::~CNumber()
{
}
// 派生类CPrimeNumber
class CPrimeNumber : public CNumber
{
private:
long n;
public:
CPrimeNumber();
CPrimeNumber(long n);
void print();
virtual ~CPrimeNumber();
};
// 派生类CPrimeNumber的实现
CPrimeNumber::CPrimeNumber()
{
}
CPrimeNumber::CPrimeNumber(long n)
{
this->n = n;
}
void CPrimeNumber::print() // 重写基类的print，在此判断n是否为素数
{
int i;
int k;
k = sqrt((double)n);
for(i = 2; i <= k; i++)
{
if(n%i == 0) break;
}
if(i > k)
{
cout << n << " is a prime number" << endl;
}
else
{
cout << n << " isn't a prime number" << endl;
}
return;
}
CPrimeNumber::~CPrimeNumber()
{
}
// 派生类CCompleteSquareNumber
class CCompleteSquareNumber : public CNumber
{
private:
long n;
public:
CCompleteSquareNumber();
CCompleteSquareNumber(long n);
void print();
virtual ~CCompleteSquareNumber();
};
// 派生类CCompleteSquareNumber的实现
CCompleteSquareNumber::CCompleteSquareNumber()
{
}
CCompleteSquareNumber::CCompleteSquareNumber(long n)
{
this->n = n;
}