lotto.cpp

我学习C++ Primer Plus过程中写下的课后作业的编程代码

//4.许多州的彩票发行机构都使用如程序清单7.4所示的简单彩票玩法的变体。
//在这些玩法中，玩家从一组被称为域号码(field number)的号码中选择几个。
//例如，可以从域号码1~47中选择5个号码：还可以从第二个间（如1~27）
//中选择一个号码（称为特选号码）。要赢得头等奖，必须正确猜中所有的号码。
//中头奖的几率是选中所有域号码几率与选中特选号码几率的乘积。请修改程序清单
//7.4，以计算中得这种彩票头奖的赃证。

//lotto.cpp--probility of winning

#include <iostream>

long double probability(unsigned numbers, unsigned picks);

int main()
{
	using namespace std;
	double total , choices;             //域号码
	double spe_total , spe_choices;     //特别号码
	cout<<"Enter the total number of choices on the game card and"<<endl;
	cout<<"the number of picks allowed in this form:"<<endl;
	cout<<"(total choices spe_total spe_choices)"<<endl;
	while ( (cin>>total>>choices>>spe_total>>spe_choices) 
		&& choices<=total && spe_choices<=spe_total  )
	{
		cout<<"You have one chance in ";
		cout<<probability(total,choices) * probability(spe_total,spe_choices);	
		cout<<" of winning.\n";
		cout<<"Next four numbers (q to quit): ";
	}
	cout<<"bye\n";
	return 0;
}

// the following function calculates the probability of picking picks
// numbers correctly from numbers choices
long double probability(unsigned numbers,unsigned picks)
{
	long double result=1.0;
	long double n;
	unsigned p;
	for(n = numbers, p = picks; p>0; n--,p--)
		result = result * n/p;
	return result;
}