题目在这里
 1 #include <stdio.h>
  2 #include <string.h>
  3 #define _MAX 10005
  4 int product[_MAX] = {0};
  5 char numOne[_MAX] = {0}, numTwo[_MAX] = {0};
  6 char numOneUp[_MAX] = {0}, numTwoUp[_MAX] = {0};    //倒序存储位置
  7 int absMax = 1;
  8 //递归进位函数
  9 void Carrying(int tag, int i, int *p)
 10 {
 11     p[i] += tag;
 12     if (p[i] > 9)
 13     {
 14         tag = 1;
 15         p[i] -= 10;
 16         Carrying(tag, i + 1, p);    //写成Carrying(tag, i, j+1, p);也成立，为了让i+j递增而已
 17     }
 18     return ;
 19 }
 20 
 21 //递归退位函数
 22 void Abdicate(int tag, int i, int *p)
 23 {
 24     p[i] += tag;
 25     if (p[i] < 0)
 26     {
 27         tag = -1;
 28         p[i] += 10;
 29         Abdicate(tag, i + 1, p);
 30     }
 31     return ;
 32 }
 33 
 34 //判断大小
 35 void size(int numOneLen, int numTwoLen)
 36 {
 37     int i, j;
 38     if (numOneLen < numTwoLen)
 39     {
 40         absMax = 2;
 41         for (i = 0; i < numTwoLen; i++)
 42         {
 43             numOneUp[i] ^= numTwoUp[i];
 44             numTwoUp[i] ^= numOneUp[i];
 45             numOneUp[i] ^= numTwoUp[i];
 46         }
 47         return ;
 48     }
 49     if (numOneLen == numTwoLen)
 50     {
 51         for (i = numOneLen - 1; i >= 0; i--)
 52         {
 53             if (numOneUp[i] < numTwoUp[i])
 54             {
 55                 absMax = 2;
 56                 for (j = 0; j < numTwoLen; j++)
 57                 {
 58                     numOneUp[j] ^= numTwoUp[j];
 59                     numTwoUp[j] ^= numOneUp[j];
 60                     numOneUp[j] ^= numTwoUp[j];
 61                 }
 62                 return ;
 63             }
 64             else if (numOneUp[i] > numTwoUp[i])
 65             {
 66                 return ;
 67             }
 68         }
 69     }
 70     return ;
 71 }
 72 
 73 //加减处理
 74 void addOrSub(int numOneLen, int numTwoLen, int flag)   //flag加法为1减法为0
 75 {
 76     int i, key = 0, tag, numLenMax, numLenMin;
 77     numOneLen = numOneLen - 1;
 78     numTwoLen = numTwoLen - 1;
 79     //数据逆序
 80     for (i = numOneLen; i > 0; i--)
 81     {
 82         numOneUp[key++] = numOne[i];
 83     }
 84     if (numOne[0] != ‘-‘)
 85     {
 86         numOneUp[key] = numOne[0];
 87         numOneLen++;
 88     }
 89     key = 0;
 90     for (i = numTwoLen; i > 0; i--)
 91     {
 92         numTwoUp[key++] = numTwo[i];
 93     }
 94     if (numTwo[0] != ‘-‘)
 95     {
 96         numTwoUp[key] = numTwo[0];
 97         numTwoLen++;
 98     }
 99     numLenMax = numOneLen > numTwoLen ? numOneLen : numTwoLen;
100     numLenMin = numOneLen < numTwoLen ? numOneLen : numTwoLen;
101     //逐位相加
102     if (flag)
103     {
104         size(numOneLen, numTwoLen);
105         for (i = 0; i < numLenMax; i++)
106         {
107             product[i] = (int)numOneUp[i] - 48;
108         }
109         for (i = 0; i < numLenMin; i++)
110         {
111             tag = (int)numTwoUp[i]-48;
112             Carrying(tag, i, product);                          //递归
113         }
114     }
115     //逐位相减
116     else
117     {
118         size(numOneLen, numTwoLen);
119         for (i = 0; i < numLenMax; i++)
120         {
121             product[i] = (int)numOneUp[i] - 48;
122         }
123         for (i = 0; i < numLenMin; i++)
124         {
125             tag = -((int)numTwoUp[i]-48);
126             Abdicate(tag, i, product);                          //递归
127         }
128     }
129 }
130 
131 //输出结果
132 void print()
133 {
134     int i, j;
135     //倒序输出结果
136     for (i = _MAX - 1; i > 0; i--)
137     {
138         if (product[i] != 0)
139         {
140             break;                               //查找到第一个不等于0的跳出
141         }
142     }
143     for (j = i; j >= 0; j--)
144     {
145         printf("%d",product[j]);
146     }
147     printf("\n");
148 }
149 
150 int main(int argc, const char * argv[])
151 {
152     int numOneLen, numTwoLen;
153 
154     scanf("%s %s",numOne,numTwo);                    //存数据
155 
156     numOneLen=(int)strlen(numOne);
157     numTwoLen=(int)strlen(numTwo);
158 
159     if (numOne[0] == ‘-‘ && numTwo[0] == ‘-‘)
160     {
161         addOrSub(numOneLen, numTwoLen, 1);
162         printf("-");
163         print();
164     }
165     else if (numOne[0] == ‘-‘ || numTwo[0] == ‘-‘)
166     {
167         addOrSub(numOneLen, numTwoLen, 0);
168         if ((numOne[0] == ‘-‘ && absMax == 1) || (numTwo[0] == ‘-‘ && absMax == 2))
169         {
170             printf("-");
171         }
172         print();
173     }
174     else
175     {
176         addOrSub(numOneLen, numTwoLen, 1);
177         print();
178     }
179     return 0;
180 }