大数加减乘除

#include <iostream>
using namespace std;
#define MAXLEN  255
int* str2int(char* str)
{
	int len = strlen(str), i;
	int * a = new int[len*sizeof(int)];
	for(i=0; i<len; ++i)
		a[i] = (int)(str[len-i-1] - '0');
	return a;
}

char* int2str(int* a,int len)
{
	int i;
	char* str = new char[(len+1)*sizeof(char)];
	for(i=0; i<len; ++i)
		str[i] = (char)(a[len-i-1] + '0');
	str[len] = '\0';
	return str;
}
//归整操作
int check(int * a, int len)
{
	int k;
	while(a[len-1] == 0 && len>1) len--;
	for(k=0; k<len; k++)
	{
		if(a[k]>=10)
		{
			a[k+1] = a[k+1] + a[k]/10;
			a[k] = a[k]%10;
		}
	}
	if(a[k]!=0) len++;
	return len;
}

char* addition(char* str1, char* str2)
{
	int len,len1,len2,i;
	len1 = strlen(str1);
	len2 = strlen(str2);
	len = (len1>=len2)?len1:len2;
	int* t1 = new int[(len+1)*sizeof(int)];
	int* t2 = new int[(len+1)*sizeof(int)];
	t1 = str2int(str1);
	t2 = str2int(str2);
	for(i=len1; i<len+1; ++i)
		t1[i] = 0;
	for(i=len2; i<len+1; ++i)
		t2[i] = 0;
	for(i=0; i<len; ++i)
		t1[i]+=t2[i];
	len = check(t1,len+1);
	return int2str(t1,len);
}

char* subtract(char* str1, char* str2)
{
	int i,len1,len2,len,flag=0;
	len1 = strlen(str1);
	len2 = strlen(str2);
	len = (len1>=len2)?len1:len2;
	char* temp = new char[len*sizeof(char)];
	char* result = new char[(len+1)*sizeof(char)];
	int* t1 = new int[len*sizeof(int)];
	int* t2 = new int[len*sizeof(int)];
	if(len1<len2 || (len1==len2)&&strcmp(str1,str2)<0)
	{
		flag = 1;
		strcpy(temp, str1);
		strcpy(str1, str2);
		strcpy(str2, temp);
		len1=strlen(str1);
		len2=strlen(str2);
	}

	t1 = str2int(str1);
	t2 = str2int(str2);
	for(i=len1; i<len; ++i) t1[i]=0;
	for(i=len2; i<len; ++i) t2[i]=0;
	for(i=0; i<len; ++i)
	{
		if(t1[i] >= t2[i]) t1[i]-=t2[i];
		else
		{
			t1[i]-=t2[i];
			int c = t1[i]*(-1)/10+1;
			t1[i] = t1[i] + c*10;
			t1[i+1] -= c;
		}
	}
	int begin=0;
	while(t1[len-1]==0 && len>1) len--;
	if(flag)
	{
		result[0] = '-';
		begin++;
		len++;
	}
	for(;begin<len; ++begin) result[begin] = (char)(t1[len-begin-1] + '0');
	result[begin] = '\0';
	return result;
}

char* multiply(char* str1, char* str2)
{
	int i,j,len,len1,len2;
	len1=strlen(str1);
	len2=strlen(str2);
	len = len1 + len2;
	int* t1 = new int[len1*sizeof(int)];
	int* t2 = new int[len2*sizeof(int)];
	int* result = new int[len*sizeof(int)];
	t1=str2int(str1);
	t2=str2int(str2);
	for(i=0; i<len; ++i)
		result[i]=0;
	for(i=0; i<len1; ++i)
		for(j=0; j<len2; ++j)
			result[i+j]+=t1[i]*t2[j];
	check(result, len);
	while(result[len-1]==0 && len>1) len--;
	return int2str(result, len);
}

void divide(char* str1, char* str2, char*& remainder, char*& quotient)
{
	int len1, len2, len, i;
	len1 = strlen(str1);
	len2 = strlen(str2);
	remainder = new char[len1*sizeof(char)];
	quotient = new char[len1*sizeof(char)];
	if(len1<len2 || ((len1==len2)&&strcmp(str1,str2)<0))
	{
		remainder = str1;
		quotient = "0";
	}
	else if(strcmp(str1,str2) == 0)
	{
		remainder = "0";
		quotient = "1";
	}
	else
	{
		int* temp = new int[len2*sizeof(int)];
		remainder[0] = '\0';
		len = strlen(remainder);
		for(i=0; i<len1; ++i)
		{
			temp[i] = 0;
			remainder[len] = str1[i];
			remainder[len+1] = '\0';
			//cout<<remainder<<endl;
			len = strlen(remainder);
			while(len > len2 ||(len==len2 && strcmp(remainder, str2)>=0))
			{
				remainder = subtract(remainder, str2);
				if(remainder[0] == '0')
					remainder[0] = '\0';
				//cout<<remainder<<endl;
				len = strlen(remainder);
				temp[i]++;
			}
			quotient[i] = (char)(temp[i] + '0');
		}
		int j = 0;
		while(quotient[j] == '0' && j<len1) j++;  //删除前导0
		for(i=0; i<len1-j; ++i)
			quotient[i] = quotient[j+i];
		quotient[len1-j] = '\0';
	}
}


int main()
{
	char str1[MAXLEN], str2[MAXLEN], str[MAXLEN];
	char* remainder,*quotient;
	cin>>str1>>str2;
	divide(str1, str2, remainder, quotient);
	//cout<<multiply(str1, str2)<<endl;
	cout<<quotient<<" "<<remainder<<endl;
	system("pause");
	return 0;
}

参考《ACM/ICPC程序设计与分析》 清华大学版。