C++實現大數類

可以用int、char、string、Bint類型初始化

支持各種運算符 

#include<bits/stdc++.h>
#define MAXN 9999
#define M 1000//
#define DLEN 4
using namespace std;
class Bint
{
	private:
		int a[M];
		int len;
	public:
		Bint()//Construction function
		{
			len=1;
			memset(a,0,sizeof(a));
		}
		Bint(const int);
		Bint(const char*);
		Bint(const Bint &);
		Bint(const std::string s);

		friend istream & operator>>(istream&,  Bint&);//Overloaded IO stream
		friend ostream & operator<<(ostream&,  Bint&);

		Bint &operator=(const Bint &);//Overloaded operator
		Bint  operator+(const Bint &) const;
		Bint  operator-(const Bint &) const;
		Bint  operator*(const Bint &) const;
		Bint  operator/(const int  &) const;
		Bint  operator^(const int  &) const;
		int   operator%(const int  &) const;

		bool operator<(const Bint& b)const
		{
			if(len!=b.len)return len<b.len;
			for (int i=len-1; i>=0; --i)if(a[i]!=b.a[i])return a[i]<b.a[i];
			return false;
		}
		bool operator>(const Bint& b)const
		{
			return b<*this;
		}
		bool operator<=(const Bint& b)const
		{
			return !(b<*this);
		}
		bool operator>=(const Bint& b)const
		{
			return !(*this<b);
		}
		bool operator!=(const Bint& b)const
		{
			return b<*this||*this<b;
		}
		bool operator==(const Bint& b)const
		{
			return !(b<*this)&&!(*this<b);
		}
		void print()//output
		{
			printf("%d",a[len-1]);
			for(int i=len-2; i>=0; --i)printf("%04d",a[i]);
			putchar('\n');
		};
};
Bint::Bint(const int b)
{
	int c,d=b;
	len=0;
	memset(a,0,sizeof(a));
	while(d>MAXN)
	{
		c=d-(d/(MAXN+1))*(MAXN+1);
		d=d/(MAXN+1);
		a[len++]=c;
	}
	a[len++]=d;
}
Bint::Bint(const char*s)
{
	int t,k,index,l,i;
	memset(a,0,sizeof(a));
	l=strlen(s);
	len=l/DLEN;
	if(l%DLEN) ++len;
	index=0;
	for(i=l-1; i>=0; i-=DLEN)
	{
		t=0;
		k=i-DLEN+1;
		if(k<0)k=0;
		for(int j=k; j<=i; j++)t=t*10+s[j]-'0';
		a[index++]=t;
	}
}
Bint::Bint(const Bint & T):len(T.len) //拷貝構造函數
{
	memset(a,0,sizeof(a));
	for(int i=0; i<len; ++i) a[i]=T.a[i];
}
Bint::Bint(const std::string s)
{
	int t,k,index,l,i;
	memset(a,0,sizeof(a));
	l=s.length();
	len=l/DLEN;
	if(l%DLEN) ++len;
	index=0;
	for(i=l-1; i>=0; i-=DLEN)
	{
		t=0;
		k=i-DLEN+1;
		if(k<0)k=0;
		for(int j=k; j<=i; j++)t=t*10+s[j]-'0';
		a[index++]=t;
	}
}
Bint & Bint::operator=(const Bint & n) //重載賦值運算符，大數之間進行賦值運算
{
	len=n.len;
	memset(a,0,sizeof(a));
	for(int i=0; i<len; ++i)a[i]=n.a[i];
	return *this;
}
istream& operator>>(istream & in,Bint & b)
{
	char ch[M*4];
	in>>ch;
	int l=strlen(ch),count=0,sum=0,i=-1;
	for(int i=l-1; i>=0;)
	{
		sum=0;
		int t=1;
		for(int j=0; j<4&&i>=0; ++j,--i,t*=10)sum+=(ch[i]-'0')*t;
		b.a[count]=sum;
		++count;
	}
	b.len=count++;
	return in;
}
ostream& operator<<(ostream& out,Bint& b) //重載輸出運算符
{
	cout<<b.a[b.len-1];
	for(int i=b.len-2; i>=0; --i)
	{
		cout.width(DLEN);
		cout.fill('0');
		cout<<b.a[i];
	}
	return out;
}
Bint Bint::operator+(const Bint & T) const
{
	Bint t(*this);
	int i,big;      //位數
	big=T.len>len?T.len:len;
	for(i=0; i<big; ++i)
	{
		t.a[i]+=T.a[i];
		if(t.a[i]>MAXN)
		{
			++t.a[i+1];
			t.a[i]-=MAXN+1;
		}
	}
	if(t.a[big]!=0)t.len=big+1;
	else t.len=big;
	return t;
}
Bint Bint::operator-(const Bint & T) const
{
	int i,j,big;
	bool flag;
	Bint t1,t2;
	if(*this>T)
	{
		t1=*this;
		t2=T;
		flag=0;
	}
	else
	{
		t1=T;
		t2=*this;
		flag=1;
	}
	big=t1.len;
	for(i=0; i<big; ++i)
		if(t1.a[i]<t2.a[i])
		{
			j=i+1;
			while(t1.a[j]==0)++j;
			--t1.a[j--];
			while(j>i)t1.a[j--]+=MAXN;
			t1.a[i]+=MAXN+1-t2.a[i];
		}
		else t1.a[i]-=t2.a[i];
	t1.len=big;
	while(t1.a[len-1]==0&&t1.len>1)--t1.len,--big;
	if(flag)t1.a[big-1]=0-t1.a[big-1];
	return t1;
}
Bint Bint::operator*(const Bint & T) const
{
	Bint ret;
	int i,j,up;
	int temp,temp1;
	for(i=0; i<len; ++i)
	{
		up=0;
		for(j=0; j<T.len; ++j)
		{
			temp=a[i]*T.a[j]+ret.a[i+j]+up;
			if(temp>MAXN)
			{
				temp1=temp-temp/(MAXN+1)*(MAXN+1);
				up=temp/(MAXN+1);
				ret.a[i+j]=temp1;
			}
			else up=0,ret.a[i + j]=temp;
		}
		if(up!=0)ret.a[i+j]=up;
	}
	ret.len=i+j;
	while(ret.a[ret.len-1]==0&&ret.len>1) --ret.len;
	return ret;
}
Bint Bint::operator/(const int & b) const
{
	Bint ret;
	int i,down=0;
	for(i=len-1; i>=0; --i)
	{
		ret.a[i]=(a[i]+down*(MAXN+1))/b;
		down=a[i]+down*(MAXN+1)-ret.a[i]*b;
	}
	ret.len=len;
	while(ret.a[ret.len-1]==0&&ret.len>1)--ret.len;
	return ret;
}
int Bint::operator %(const int & b) const
{
	int i,d=0;
	for (i=len-1; i>=0; --i)d=((d*(MAXN+1))%b+a[i])%b;
	return d;
}
Bint Bint::operator^(const int & n) const
{
	Bint t,ret(1);
	if(n<0)exit(-1);
	if(n==0)return 1;
	if(n==1)return *this;
	int m=n,i;
	while(m>1)
	{
		t=*this;
		for(i=1; i<<1<=m; i<<=1)t=t*t;
		m-=i;
		ret=ret*t;
		if(m==1)ret=ret*(*this);
	}
	return ret;
}