大数算法

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
const int maxnum = 100;

using namespace std;

int a[maxnum], b[maxnum];

void BigNumber_add(int a[], int b[], int n1, int n2)
{
     int tmp = max(n1, n2);
   for(int i = 0; i < tmp; i++){
          a[i] += b[i];
          if(a[i] > 9){
          a[i] -= 10;
          a[i+1]++;
          }
   }
   int flag = 0;
   for(int i = tmp; i >= 0; i--)
        if(a[i] != 0){
         flag = i;
          break;
        }

      for(int i = flag; i >= 0; i--)
         cout << a[i];

}

int main()
{         string s1, s2;
          cin >> s1 >> s2;
      int n1 = s1.length();
      int n2 = s2.length();
      memset(a, 0, sizeof(a));
      memset(b, 0, sizeof(b));
      for(int i = 0; i < n1; i++)
          a[i] = s1[n1-i-1] - '0';
      for(int i = 0; i < n2; i++)
          b[i] = s2[n2-i-1] - '0';
    BigNumber_add(a, b, n1, n2);// test add
    return 0;
}

#include <iostream>
#include <cstring>
#include <string>
#include <cstdio>
using namespace std;
const int maxnum = 100;
void BigNumber_sub(char *s1, char *s2)
{

}
int compare(char *s1, char *s2)
{
          int n1 = strlen(s1);
          int n2 = strlen(s2);
          if(n1 > n2)
                    return 1;
          else if(n1 < n2)
                    return -1;
               else if(n1 == n2)
                    return strcmp(s1, s2);
}
void stio(char *str, int *a)
{           int tmp = strlen(str);
          for(int i = 0; i < tmp; i++)
              a[i] = str[tmp-i-1] - '0';
}
void print(int *c, int n, int maxlen){
        if(n < 0)
          cout << "-";
          int flag = 0;
    for(int i = maxlen-1; i >= 0; i--){
          if(c[i] != 0)
           flag = 1;
           if(flag || i == 0)
          cout << c[i];
    }
    cout << endl;
}
int main()
{
          char s1[maxnum], s2[maxnum];

   while(cin >> s1 >> s2){
         int a[maxnum]={0}, b[maxnum]={0}, c[maxnum];
          int t1 = strlen(s1), t2 = strlen(s2);
          int maxlen = t1>t2? t1: t2;
          int cmp = compare(s1, s2);
          stio(s1, a);
          stio(s2, b);
          for(int i = 0; i < maxlen; i++){
                    if(cmp >= 0){
                     if(a[i] >= b[i])
                        c[i] = a[i] - b[i];
                     else{
                      c[i] = a[i]-b[i]+10;
                      a[i+1]--;
                      }
            } else
                   {
                    if(b[i] >= a[i])
                     c[i] = b[i]-a[i];
                   else{
                      c[i] = b[i] -a[i]+10;
                      b[i+1]--;
                    }
                 }
  }
       print(c, cmp, maxlen);
}
   return 0;
}