面试题大数相加相减

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根据http://www.cnblogs.com/caixu/archive/2011/09/26/2192189.html这个修改了相加函数，并增加了相减函数。

#include <iostream>

#include <string>

using namespace std;

const int MAX_LENGTH = 1000;

class ds
{
public:
   void add(string x, string y);
   void sub(string x, string y);
   private :
   string s1,s2;

};

void ds::sub(string x, string y)
{
   int length1 = x.length();
   int length2 = y.length();
   int long_length;
   int short_length;

   string bigger_string;
   string smaller_string;

   int i = 0;
   int big = -1;
   if (length1 > length2) {
   bigger_string = x;
   smaller_string = y;
   long_length = length1;
   short_length = length2;
   } else if (length1 < length2) {
   bigger_string = y;
   smaller_string = x;
   long_length = length2;
   short_length = length1;
   big = 2;
   } else {
   for (i = 0; i< length1; i++) {
   int sub_value = x[length1-1-i] - y[length1-1-i];
   if(sub_value > 0) {
   bigger_string = x;
   smaller_string = y;
   big = 0;
   break;
   }
   else if (sub_value < 0) {
   bigger_string = y;
   smaller_string = x;
   big = 1;
   break;
   }
   else{}

   }

   if (-1 == big) {
   cout << "0" << endl;
   return;
   }
   }

   int sub = 0;
   int flag = 0;
   int sub_sum[MAX_LENGTH];
   for (i = 0; i<short_length;i++) {
   sub = bigger_string[long_length-1-i] - smaller_string[short_length-1-i];
   if (sub <0) {
   sub += 10;
   flag = 1;
   } else {
   flag = 0;
   }
   if(1 == flag)
   bigger_string[long_length-1-i-1] -= ('1' - '0');
   sub_sum[i] = sub;
   }

   for(i; i<long_length; i++) {
   sub_sum[i] = bigger_string[long_length-1-i] - '0';
   }

   if ( big > 0) {
   cout << "-";
   }

   int str_flag = 0;
   for (i--; i>=0;i--) {
   if (0 == str_flag &&(0 == (sub_sum[i] - '0')))
   ;
   else
   cout << sub_sum[i];
   }
}

void ds::add(string x, string y)
{
   int flag = 0;
   int i;
   int length1 = x.length();
   int length2 = y.length();
   string long_string;
   string short_string;
   int short_length;
   int long_length;

   if (length1 >length2) {
   long_string = x;
   short_string = y;
   short_length = length2;
   long_length = length1;
   }
   else {
   long_string = y;
   short_string = x;
   short_length = length1;
   long_length = length2;
   }

   cout << "long is " << long_string << "length is " << long_length << ", short is " << short_string << ",short length is " << short_length<<endl;
   int add_sum[MAX_LENGTH];
   int sum = 0;

   for (i = 0; i<short_length;i++) {
   sum = long_string[long_length-1-i] - '0' + short_string[short_length-1-i] - '0' + flag;
   if (sum >= 10) {
   sum -= 10;
   flag = 1;
   } else {
   flag = 0;
   }
   add_sum[i] = sum;
   }

   for (; i<long_length;i++) {
   sum = long_string[long_length-1-i] - '0' + flag;
   if (sum >= 10) {
   sum -= 10;
   flag = 1;
   } else {
   flag = 0;
   }
   add_sum[i] = sum;
   }

   if (flag == 1)
   add_sum[i++] = 1;

   for(i=i--;i>= 0;i--)
   cout << add_sum[i];
}

int main()
{
   ds dashu;
   string x1,x2;
   cout<<"please input two word:" <<endl;
   cin >>x1>>x2;
   int n1=x1.length();
   int n2=x2.length();
   if (n1==n2)
   dashu.equal(x1,x2,n1,n2);
   else
   dashu.nequal(x1,x2,n1,n2);

   dashu.add(x1, x2);
   cout <<endl;
   cout<<"please input two word:" <<endl;
   cin >>x1>>x2;
   dashu.sub(x1, x2);
   cout <<endl;
   return 0;
}