普通的大数运算

只写了加减，乘除不太明白T_T..弄明白补上。

  1 #include <stdio.h>
  2 #include <string.h>
  3 
  4 #define MAX 1000
  5 
  6 void Add(char *str1,char *str2, char *str3);
  7 void Minus(char *str1, char *str2, char *str3);
  8 void Times(char *str1, char *str2, char *str3);
  9 
 10 int main(void)
 11 {
 12     char str1[MAX], str2[MAX], str3[MAX+10];
 13 
 14     scanf("%s %s", str1, str2);
 15 
 16     //To do
 17 
 18     printf("%s\n", str3);
 19 
 20     return 0;
 21 }
 22 
 23 void Add(char *str1,char *str2, char *str3)
 24 {
 25     int i, j, i1, i2, len1, len2, cnt, tmp;
 26     char ch;
 27 
 28     len1 = strlen(str1);
 29     len2 = strlen(str2);
 30 
 31     i1 = len1-1;
 32     i2 = len2-1;
 33 
 34     j = cnt = 0;   //cnt是进位
 35 
 36 
 37 
 38     for ( ; i1>=0 && i2>=0; i1--, i2--, j++)
 39     {
 40         tmp = str1[i1]-'0'+str2[i2]-'0' + cnt;
 41         str3[j] = tmp % 10 + '0';
 42         cnt = tmp / 10;
 43     }
 44     while (i1 >= 0)
 45     {
 46         tmp = str1[i1--] - '0' + cnt;
 47         cnt = tmp / 10;
 48         str1[j++] = tmp % 10 + '0';
 49     }
 50     while (i2 >= 0)
 51     {
 52         tmp = str2[i2--] - '0' + cnt;
 53         cnt = tmp / 10;
 54         str2[j++] = tmp % 10 + '0';
 55     }
 56     if (cnt)
 57     {
 58         str3[j++] = cnt + '0';
 59     }
 60     str3[j] = '\0';
 61 
 62     for (i=0, j--; j>i; i++, j--)
 63     {
 64         ch = str3[j];
 65         str3[j] = str3[i];
 66         str3[i] = ch;
 67     }
 68 }
 69 
 70 void Minus(char *str1, char *str2, char *str3)
 71 {
 72     //need str1 > str2
 73     int i, j, len, i1, i2, cnt, tmp;
 74     char ch;
 75 
 76     i1 = strlen(str1) - 1;
 77     i2 = strlen(str2) - 1;
 78 
 79     j = cnt = 0;
 80 
 81     while (i2 >= 0)
 82     {
 83         tmp = str1[i1]-str2[i2]-cnt;
 84         if (tmp < 0)
 85         {
 86             str3[j] = tmp + 10 + '0';
 87             cnt = 1;
 88         }
 89         else
 90         {
 91             str3[j] = tmp + '0';
 92             cnt = 0;
 93         }
 94         i2--;
 95         i1--;
 96         j++;
 97     }
 98     while (i1 >= 0)
 99     {
100         tmp = str1[i1] - '0' - cnt;
101         if (tmp < 0)
102         {
103             str3[j] = tmp + 10 + '0';
104             cnt = 1;
105         }
106         else
107         {
108             str3[j] = tmp + '0';
109             cnt = 0;
110         }
111         i1--;
112         j++;
113     }
114     j--;
115     //去0
116     while (str3[j] == '0' && j>0)
117     {
118         j--;
119     }
120     str3[++j] = '\0';
121 
122 
123     for (i=0, j--; i < j; i++, j--)
124     {
125         ch = str3[i];
126         str3[i] = str3[j];
127         str3[j] = ch;
128     }
129 }