大数四则运算java（转）

 // 大数的四则运算
 #include <iostream>
 #include <string>
 #include <algorithm>
 using namespace std;

 class BIGINTEGEROPERATIONS
 {
 private:
     static int COMPARE(string number1, string number2)
     {
         int j;

         int length1 = number1.size();
         int length2 = number2.size();

         if(number1.size() == 0) number1 = "0";
         if(number2.size() == 0) number2 = "0";

         j = 0;
         for(int i = 0; i < length1; ++i)
         {
             if(number1[i] == '0') ++j;
             else break;
         }
         number1 = number1.substr(j);

         j = 0;
         for(int i = 0; i < length2; ++i)
         {
             if(number2[i] == '0') ++j;
             else break;
         }
         number2 = number2.substr(j);

         length1 = number1.size();
         length2 = number2.size();

         if(length1 > length2)
         {
             return 1;
         }
         else if(length1 == length2)
         {
             if(number1.compare(number2) > 0)
             {
                 return 1;
             }
             else if(number1.compare(number2) == 0)
             {
                 return 0;
             }
             else
             {
                 return -1;
             }
         }
         else
         {
             return -1;
         }

         return 0;
     }

 public:
     static string PLUS(string number1,string number2)
     {
         int i;
         int length1 = number1.size();
         int length2 = number2.size();

         string result="";

         reverse(number1.begin(), number1.end());
         reverse(number2.begin(), number2.end());

         for(i = 0; i < length1 && i < length2; i++)
         {
             char c = (char)(number1[i] + number2[i] - 48);
             result = result + c;
         }

         while(i < length1)
         {
             result = result + number1[i];
             ++i;
         }

         while(i < length2)
         {
             result = result + number2[i];
             ++i;
         }

         int carry = 0;
         for(i = 0; i < (int)result.size(); ++i)
         {
             int value = result[i] - 48 + carry;
             result[i] = (char)(value % 10 + 48);
             carry = value / 10;
         }

         if(carry !=0 )
         {
             result = result + (char)(carry + 48);
         }

         for(i = result.size() - 1; i >= 0; i--)
         {
             if(result[i] != '0') break;
         }

         result = result.substr(0, i + 1);

         reverse(result.begin(), result.end());
         if(result.length() == 0) result = "0";
         return result;
     }

     static string MINUS(string number1,string number2)
     {
         int i;
         string result = "";

         int length1 = number1.size();
         int length2 = number2.size();

         if(COMPARE(number2,number1) > 0)
         {
             return "-" + MINUS(number2, number1);
         }

         reverse(number1.begin(),number1.end());
         reverse(number2.begin(),number2.end());

         for(i = 0; i < length1 && i < length2; i++)
         {
             char c = number1[i] - number2[i] + 48;
             result = result + c;
         }

         if(i < length1)
         {
             for(; i < length1; i++)
             {
                 result = result + number1[i];
             }
         }

         int carry = 0;
         for(i = 0; i < (int)result.length(); i++)
         {
             int value = result[i] - 48 + carry;
             if(value < 0)
             {
                 value = value + 10;
                 carry = -1;
             }
             else carry = 0;
             result[i]=(char)(value + 48);
         }

         for(i = result.size() - 1; i >= 0; i--)
         {
             if(result[i] != '0')break;
         }

         result = result.substr(0, i+1);

         reverse(result.begin(), result.end());
         if(result.length()==0) result = "0";
         return result;
     }

     static string MULTIPLY(string number1, string number2)
     {
         int i, j;
         int *iresult;
         int length1 = number1.size();
         int length2 = number2.size();
         string result = "";

         reverse(number1.begin(), number1.end());
         reverse(number2.begin(), number2.end());

         iresult = (int*)malloc(sizeof(int) * (length1 + length2 + 1));
         memset(iresult, 0, sizeof(int) * (length1 + length2 + 1));

         for(i = 0; i < length1; i++)
         {
             for(j = 0; j < length2; j++)
             {
                 iresult[i+j] += ((number1[i] - 48) * (number2[j] - 48));
             }
         }

         int carry = 0;
         for(i = 0; i < length1 + length2; i++)
         {
             int value = iresult[i] + carry;
             iresult[i] = value % 10;
             carry = value / 10;
         }

         for(i = length1 + length2 - 1; i >= 0; i--)
         {
             if(iresult[i] != 0)break;
         }

         for(; i >= 0; i--)
         {
             result = result + (char)(iresult[i]+48);
         }

         free(iresult);

         if(result == "") result = "0";
         return result;
     }

     // 缺省地，商数向下取整， floatpoint用于指定保留小数点的位数
     static string DIVIDE(string number1, string number2, int floatpoint = 0)
     {
         int i, j, pos;
         string result = "";
         string tempstr = "";
         int length1 = number1.size();
         int length2 = number2.size();

         if((COMPARE(number2, number1) > 0) && (floatpoint == 0))
         {
             return "0";
         }

         tempstr = number1.substr(0, length2);
         pos = length2 - 1;

         while(pos < length1)
         {
             int quotient = 0;
             while(COMPARE(tempstr, number2) >= 0)
             {
                 quotient++;
                 tempstr = MINUS(tempstr, number2);
             }

             result = result + (char)(quotient + 48);
             pos++;
             if(pos < length1)
             {
                 tempstr += number1[pos];
             }
         }

         if(floatpoint > 0)
         {
             result += '.';
             string stmp = "1";
             int itmp = 0;
             for(int k = 0; k < floatpoint; ++k)
             {
                 stmp += '0';
                 if(COMPARE(MULTIPLY(MINUS(number1, MULTIPLY(DIVIDE(number1, number2), number2)), stmp), number2) < 0)
                 {
                     result += '0';
                     ++itmp;
                 }
             }

             string temp = DIVIDE(MULTIPLY(MINUS(number1, MULTIPLY(DIVIDE(number1, number2), number2)), stmp), number2);
             if(temp[0] != '0') result += temp;
         }

         j = result.size();
         for(i = 0; i < j; i++)
         {
             if(result[i] != '0') break;
         }

         result = result.substr(i, j);

         return result;
     }

     static string MOD(string number1, string number2)
     {
         if(COMPARE(number2, number1) > 0)
         {
             return number1;
         }
         else if(COMPARE(number2, number1) == 0)
         {
             return "0";
         }
         else
         {
             return MINUS(number1, MULTIPLY(DIVIDE(number1, number2), number2));
         }
     }
 };

 int main(int argc, char* argv[])
 {
     string str1 = "9999999999999999999999999999999999999999";
     string str2 = "9998999899989998999899989998999899989998";

     cout << BIGINTEGEROPERATIONS::PLUS(str1, str2) << endl;
     cout << "===============" << endl;
     cout << BIGINTEGEROPERATIONS::MINUS(str1, str2) << endl;
     cout << "===============" << endl;
     cout << BIGINTEGEROPERATIONS::MULTIPLY(str1, str2) << endl;
     cout << "===============" << endl;
     cout << BIGINTEGEROPERATIONS::DIVIDE(str1, str2, 4) << endl;
     cout << "===============" << endl;
     cout << BIGINTEGEROPERATIONS::MOD(str1, str2) << endl;

     return 0;
 }