inRange()这个函数如何实现，反迭代为何就能判断阶乘计算结果是否超最大值
#include <iostream>#include <climits>
class Factorial
{
public:
Factorial(unsigned short num);
unsigned long getFactorial();
bool inRange();
private:
unsigned short num;
};
Factorial::Factorial(unsigned short num)
{
this->num = num;
}
unsigned long Factorial::getFactorial()
{
unsigned long sum = 1;
for( int i=1; i <= num; i++ )
{
sum *= i;
}
return sum;
}
bool Factorial::inRange()
{
unsigned long max = ULONG_MAX;
for( int i=num; i >= 1; --i )
{
max /= i;
}
if( max < 1 )
return false;
else
return true;
}
int main()
{
unsigned short num = 0;
std::cout << "请输入一个整数: ";
std::cin >> num;
Factorial fac(num);
if( fac.inRange() )
{
std::cout << num << "的阶乘值是" << fac.getFactorial() << "\n\n";
}
else
{
std::cout << "您所输入的值太大!\n\n";
}
return 0;
}
简单的移项啊
max=ulong_max/1/2/3/4/.../num=ulong_max/(1*2*3*..*num)=ulong_max/(num!);
max<1 ==> ulong_max<num!;
所以溢出
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