大数的阶乘.cpp

大数相乘的源代码,使用C++在VC环境中实现.

//vl_app.cpp
//calculates factorrials of larger numbers using verylong class
#include"verylong.h"

void verylong::putvl() const
{
	char temp[SZ];
	strcpy(temp,vlstr);
	cout << strrev(temp);
}

void verylong::getvl()
{
	cin>>vlstr;
	vlen=strlen(vlstr);
	strrev(vlstr);
}

verylong verylong::operator +(const verylong v)
{
	char temp[SZ];
	int j;
	int maxlen=(vlen>v.vlen)? vlen:v.vlen;
	int carry=0;
	for(j=0;j<maxlen;j++)
	{
		int d1=(j>vlen-1)?0:vlstr[j]-'0';
		int d2=(j>v.vlen-1)?0:v.vlstr[j]-'0';
		int digitsum=d1+d2+carry;
		if(digitsum>=10)
		{
			digitsum-=10;
			carry=1;
		}
		else 
			carry=0;
		temp[j]=digitsum='0';
	}
	if(carry==1)
		temp[j++]='1';
	temp[j]='\0';
	return verylong(temp);
}
verylong verylong::operator *(const verylong v)
{
	verylong pprod;
	verylong tempsum;
	for(int j=0;j<v.vlen;j++)
	{
		int digit=v.vlstr[j]-'0';
		pprod=multdigit(digit);
		for(int k=0;k<j;k++)
			pprod=mult10(pprod);
		tempsum=tempsum+pprod;
	}
	return tempsum;
}

verylong verylong::mult10(const verylong v)const
{
	char temp[SZ];
	for(int j=v.vlen-1;j>=0;j--)
		temp[j+1]=v.vlstr[j];
	temp[0]='0';
	temp[v.vlen+1]='\0';
	return verylong(temp);
}
verylong verylong::multdigit(const int d2)const
{
	char temp[SZ];
	int j,carry=0;
	for(j=0;j<vlen;j++)
	{
		int d1=vlstr[j]-'0';
		int digitprod=d1*d2;
		digitprod+=carry;
		if(digitprod>=10)
		{
			carry=digitprod/10;
			digitprod-=carry*10;
		}
		else
			carry=0;
		temp[j]=digitprod+'0';
	}
	if(carry!=0)
		temp[j++]='\0';
	temp[j]='\0';
	return verylong(temp);
}

int main()
{
	unsigned long numb,j;
	verylong fact=1;						//initialize verylong

	cout<<"Enter number: ";
	cin>>numb;								//input a long int

	for(j=numb;j>0;j--)						//factorial is numb *
		fact=fact*j;						//numb-1 * numb-2*
	cout<<"Factorial is=";					//numb-3 and so on
	fact.putvl();							//display factorial
	cout<<endl;
	return 0;
}