个人实现的大数模板（加、乘）

目前实现大数的加法及乘法，实现了几个OJ的题目作为测试，若有错误多指正。

 

#include <iostream>
#include <string>
#include <cstring>

/************************************************************************/
/*              大数运算模板，暂时实现大数加、乘法                        */
/************************************************************************/
class BigInteger{
public:
	BigInteger():length(0),isNegative(false),digit(NULL){};
	BigInteger(const std::string &num);
	BigInteger(const BigInteger& old);
	int getLength(void){return length;};

	~BigInteger(){if(NULL != digit) delete []digit;};

	friend std::ostream& operator<<(std::ostream&, const BigInteger&);
	
	BigInteger& operator+=(const BigInteger& addend);
	friend BigInteger operator+(const BigInteger&, const BigInteger&);
	
	BigInteger& operator*=(const BigInteger& multiplier);
	friend BigInteger operator*(const BigInteger&, const BigInteger&);
	friend BigInteger operator*(const BigInteger&, const int);
	friend BigInteger operator*(const int, const BigInteger&);

	const int& operator[](const int t);

	BigInteger& operator=(const BigInteger&);
	BigInteger& operator=(const char*);
	BigInteger& operator=(const std::string&);
	BigInteger& operator=(const int);

private:
	int length;
	bool isNegative;
	int* digit;  //the smallest number storage in digit[0]
};

BigInteger::BigInteger(const std::string &num){
	if(num[0] == '-'){
		isNegative = true;
		length = num.length() - 1;
	}
	else{
		isNegative = false;
		length = num.length();		
	}

	digit = new int[length];	
	int i, numLen = num.length();
	for(i = 0; i < length; i++){
		digit[i] = num[numLen-1-i] - '0';
	}	
}


BigInteger::BigInteger(const BigInteger& old){
	length = old.length;
	isNegative = old.isNegative;
	digit = new int[length];
	int i;
	for(i = 0; i < length; i++){
		digit[i] = old.digit[i];
	}
}

BigInteger& BigInteger::operator+=(const BigInteger& addend){//hadn't consider - this time
	int maxLen = length > addend.length ? length : addend.length;
	int* sum = new int[maxLen + 1];
	int i, carry = 0;

	for(i = 0; i < length && i < addend.length; i++){
		sum[i] = digit[i] + addend.digit[i] + carry;
		if(sum[i] >= 10){
			sum[i] -= 10;
			carry = 1;
		}else{
			carry = 0;
		}
	}
	if(i >= length){
		for(; i < addend.length; i++){
			sum[i] = addend.digit[i] + carry;
			if(sum[i] >= 10){
				sum[i] -= 10;
				carry = 1;
			}else{
				carry = 0;
			}
		}
	}
	else{
		for(; i < length; i++){
			sum[i] = digit[i] + carry;
			if(sum[i] >= 10){
				sum[i] -= 10;
				carry = 1;
			}else{
				carry = 0;
			}
		}
	}

	if(carry){
		sum[i] = carry;
		delete []digit;
		digit = sum;
		length = maxLen + 1;
	}
	else{
		delete []digit;
		length = maxLen;
		digit = new int[length];
		for(i = 0; i < maxLen; i++){
			digit[i] = sum[i];
		}
		delete []sum;
	}

	return *this;
}

BigInteger operator+(const BigInteger& a, const BigInteger& b){
	BigInteger ans(a);
	ans += b;
	return ans;
}

BigInteger& BigInteger::operator*=(const BigInteger& multiplier){
	isNegative = !(isNegative == multiplier.isNegative);

	int maxLen = length + multiplier.length, ansLen = 0;
	int *product = new int[maxLen];

	int i, t;
	memset(product, 0, sizeof(int)*maxLen);
	for(i = 0; i < length; i++){
		for(t = 0; t < multiplier.length; t++){
			product[i+t] += digit[i]*multiplier.digit[t];
		}
	}

	for(i = 0; i < maxLen-1; i++){
		product[i+1] += product[i]/10;
		product[i] %= 10;
	}

	ansLen = maxLen - 1;
	while(ansLen > 0 && product[ansLen] == 0){
		ansLen--;
	}

	length = ansLen + 1;
	if(length == maxLen){
		delete []digit;
		digit = product;
	}else{
		delete []digit;
		digit = new int[length];
		int k;
		for(k = 0; k < length; k++){
			digit[k] = product[k];
		}
		delete []product;
	}
	return *this;
}

BigInteger operator*(const BigInteger& a, const BigInteger& b){
	BigInteger ans(a);
	ans *= b;
	return ans;
}

const int& BigInteger::operator[](const int t){
	if(NULL==digit || t>=length){
		return -1;
	}
	else{
		return digit[t];
	}
}

std::ostream& operator<<(std::ostream& os, const BigInteger& b_int){
	if(b_int.isNegative){
		if(!(b_int.length==1 && b_int.digit[0]==0)){
			os<<'-';
		}//if b_int == 0 do not output -0
	}
	int i;
	for(i = b_int.length-1; i >= 0; i--){
		os<<b_int.digit[i];
	}
	return os;
}

BigInteger& BigInteger::operator=(const BigInteger& old){
	if(this != &old){
		length = old.length;
		isNegative = old.isNegative;
		delete []digit;
		digit = new int[length];
		int i;
		for(i = 0; i < length; i++){
			digit[i] = old.digit[i];
		}
	}
	return *this;
}

BigInteger& BigInteger::operator=(const char* number){
	if(number[0] != '-'){
		isNegative = false;
		length = strlen(number);
	}
	else{
		isNegative = true;
		length = strlen(number)-1;
	}
	
	if(digit != NULL) delete []digit;
	digit = new int[length];
	int i, numLen = strlen(number);
	for(i = 0; i < length; i++){
		digit[i] = number[numLen-1-i] - '0';
	}
	return *this;
}

BigInteger& BigInteger::operator=(const std::string& number){
	if(number[0] != '-'){
		isNegative = false;
		length = number.length();
	}
	else{
		isNegative = true;
		length = number.length() - 1;
	}

	if(digit != NULL) delete []digit;
	digit = new int[length];
	int i, numLen = number.length();
	for(i = 0; i < length; i++){
		digit[i] = number[numLen-1-i] - '0';
	}
	return *this;
}

BigInteger& BigInteger::operator=(const int number){
	isNegative = number < 0 ? true : false;
	
	int tmp = number<0 ? -number : number;
	length = 0;
	do{
		length++;
		tmp /= 10;
	}while(tmp);

	if(NULL != digit){
		delete []digit;
	}
	digit = new int[length];
	tmp = number<0 ? -number : number;
	int i = 0;
	do{
		digit[i++] = tmp%10;
		tmp /= 10;
	}while(tmp);

	return *this;
}


int main(){
/*	
//hdu1002
    int t, k = 0;
	std::cin>>t;
	for(k = 1; k <= t; k++){
		if(k != 1){
			std::cout<<std::endl;
		}

		std::string str_a, str_b;
		std::cin>>str_a>>str_b;
		BigInteger a(str_a);
		BigInteger b(str_b);
		BigInteger ans(a);

		ans = a + b;
		std::cout<<"Case "<<k<<":"<<std::endl;
		std::cout<<a<<" + "<<b<<" = "<<ans<<std::endl;
	}
*/

/*
//hdu1715
	BigInteger a[1001];
	a[0] = "0";
	a[1] = "1";
	int t;
	for(t = 2; t <= 1000; t++){
		a[t] = a[t-1] + a[t-2];
	}

	int i, n;
	std::cin>>n;
	while(n--){
		std::cin>>i;
		std::cout<<a[i]<<std::endl;
	}
	*/
/*
	//poj 1503
	BigInteger ans, big;
	ans = "0";
	char num[120];
	while(std::cin>>num){
		if(num[0] == '0' && strlen(num)==1){
			break;
		}
		big = num;
		ans += big;
	}
	std::cout<<ans<<std::endl;
*/
/*
	//poj 1001 unfinish====
	BigInteger ans, big;
	int n;
	std::string num;
	char *pnum;
	while(std::cin>>num>>n){
		big = num;
		pnum = new char[num.length()];
		int i, iDecimal;
		for(i = 0; i < num.length){
		}
		ans = "1";
		while(n){
			if(n&1){
				ans *= big;
			}
			big *= big;
			n >>= 1;
		}
		std::cout<<ans<<std::endl;
	}
*/
	/*
	//poj 2389
	BigInteger ans, big;
	std::string n1, n2;
	std::cin>>n1>>n2;
	ans = n1, big = n2;
	ans *= big;
	std::cout<<ans<<std::endl;
	*/
/*
	//poj 3331
	const int MAXDAY = 367;
	BigInteger factorial[MAXDAY];
	int i;
	factorial[0] = 1;
	for(i = 1; i < MAXDAY; i++){
		factorial[i] = i;
		factorial[i] *= factorial[i-1];
	}
	int t, day, n, ans = 0;
	std::cin>>t;
	while(t--){
		std::cin>>day>>n;
		ans = 0;
		for(i = 0; i < factorial[day].getLength(); i++){
			if(factorial[day][i] == n){
				ans++;
			}
		}
		std::cout<<ans<<std::endl;
	}
*/
/*	//acm.zjut.edu.cn http://172.16.7.252/ShowProblem.aspx?ShowID=1027
	BigInteger a, b;
	std::string str_a, str_b;
	while(std::cin>>str_a>>str_b){
		a = str_a;
		b = str_b;
		a *= b;
		std::cout<<a<<std::endl;
	}*/

	//acm.zjut.edu.cn http://172.16.7.252/ShowProblem.aspx?ShowID=1217
	BigInteger a, b;
	std::string str_a, str_b;
	//char str_a[400], str_b[400];
	while(std::cin>>str_a>>str_b){
		if(str_a=="0" && str_b=="0"){
			break;
		}
		if(str_a=="0" || str_b=="0"){
			std::cout<<"0"<<std::endl;
			continue;
		}
		a = str_a;
		b = str_b;
		a *= b;
		std::cout<<a<<std::endl;
	}/**/

}