#include <stdio.h>
#include<string.h>
#include <stdlib.h>
#define MAX 101

void bigDataAdd(char a[], char b[]);
int main()
{
      char a[MAX] = {0};
      char b[MAX] = {0};
      gets(a);
      gets(b);
      bigDataAdd(a,b);
      return 0;
}
void bigDataAdd(char a[], char b[])
{
      int length = 0;
      int m = 0;
      char sum[MAX+1];
      char tempA[MAX] = {0};
      char tempB[MAX] = {0};
      int jin = 0;
      int lengthA = strlen(a);
      int lengthB = strlen(b);
      length = lengthA > lengthB ? lengthA : lengthB;
      // 将字符串翻转
      for(m=0;m<length;m++)
      {
            if (lengthA == length) {
                  tempA[m] = a[lengthA-1-m];
                  if (m < lengthB) {
                        tempB[m] = b[lengthB-1-m];
                  } else {
                        tempB[m] = '0';
                  }
            } else if (lengthB == length) {
                  tempB[m] = b[lengthB-1-m];
                  if (m < lengthA) {
                        tempA[m] = a[lengthA-1-m];
                  } else {
                        tempA[m] = '0';
                  }
            }
      }

      // 相加
      for(m=0;m<length;m++)
      {
            sum[m] = (tempA[m] - '0' + (tempB[m] - '0') + jin) % 10 + '0';
            jin = (tempA[m] - '0' + (tempB[m] - '0') + jin) / 10;
      }

      for(m=0;m<length;m++)
      {
           printf("%c", sum[length - 1 - m]);
      }
}

参考：http://blog.csdn.net/insistgogo/article/details/6581466

http://www.cnblogs.com/Lyush/archive/2011/08/14/2137721.html