大数加减运算

  1 #include<iostream>
  2 #include<string>
  3 
  4 using namespace std;
  5 
  6 void BDplus(string str1, string str2)
  7 {
  8     int len1 = str1.length();
  9     int len2 = str2.length();
 10     char *value = NULL;
 11     if (len1 >= len2)
 12     {
 13         //value= (char*)malloc(len1*sizeof(char));
 14         value = new char[len1*sizeof(char)+1];
 15     }
 16     else if (len1 <= len2)
 17     {
 18         //value = (char*)malloc(len2*sizeof(char));
 19         value = new char[len2*sizeof(char)+1];
 20     }
 21     int flag = 0;
 22 
 23     int i = 0;
 24     while (len1 > 0 && len2 > 0)
 25     {
 26         if (len1 <= 0 && len2 > 0)
 27         {
 28             len1 = 1;
 29             str1[0] = ‘0‘;
 30         }
 31         else if (len1 > 0 && len2 <= 0)
 32         {
 33             len2 = 1;
 34             str2[0] = ‘0‘;
 35         }
 36         int temp;
 37         temp = (int)(str1[len1 - 1] - ‘0‘) + (int)(str2[len2 - 1] - ‘0‘); 
 38         value[i++] = (char)(temp % 10 + flag + (int)‘0‘);
 39         if (temp / 10 == 1)
 40         {
 41             flag = 1;
 42         }
 43         else
 44         {
 45             flag = 0;
 46         }
 47         len1--;
 48         len2--;
 49     }
 50     if (flag == 1)
 51     {
 52         value[i++] = ‘1‘;
 53         value[i] = ‘\0‘;
 54     }
 55     else
 56     {
 57         value[i] = ‘\0‘;
 58     }
 59     i--;
 60     for(; i >= 0; i--)
 61     {
 62         cout << value[i];
 63     }
 64 }
 65 void BDminus(string str1, string str2)
 66 {
 67     int len1, len2;
 68     len1 = str1.length();
 69     len2 = str2.length();
 70     int flag = 0, i = 0;
 71     int Case = 0;
 72     char *value = NULL;
 73 
 74     /*因为 string类重载了与string相比较的所有函数，包括<,>,==,>=,<=,!=*/
 75 
 76     //if (len1 == len2)//两字符串长度相等
 77     //{
 78     //    int j = 0;
 79     //    while ((j < len1) && (str1[j] == str2[j]))
 80     //    {
 81     //        j++;
 82     //    }
 83     //    if (j >= len1)//字符串1等于字符串2
 84     //    {
 85     //        Case = 1;
 86     //    }
 87     //    else        //字符串1不等于字符串2
 88     //    {
 89     //        if (str1[j]>str2[j])//字符串1大于字符串2
 90     //        {
 91     //            Case = 1;
 92     //        }
 93     //        else                //字符串1小于字符串2
 94     //        {
 95     //            Case = 2;
 96     //        }
 97     //    }
 98 
 99     //}
100     //else if (len1 > len2)//字符串1长度大于字符串2
101     //{
102     //    Case = 1;
103     //}
104     //else                //字符串1长度小于字符串2
105     //{
106     //    Case = 2;
107     //}
108 
109     if(str1>=str2)// (Case==1)//情况一 大减小
110     {
111         value = (char *)malloc(len1*sizeof(char));
112         int temp;
113         while (len1 > 0 && len2 > 0)
114         {
115             if (flag == 1)//借位处理
116             {
117                 if (str1[len1 - 1] == ‘0‘)
118                 {
119                     str1[len1 - 1] = ‘9‘;
120                     flag = 1;
121                 }
122                 else if (str1[len1 - 1] != ‘0‘)
123                 {
124                     str1[len1 - 1] = str1[len1 - 1] - 1;
125                     flag = 0;
126                 }
127             }
128             if (str1[len1 - 1] >= str2[len2 - 1])
129             {
130                 temp = (str1[len1 - 1] - ‘0‘) - (str2[len2 - 1] - ‘0‘);
131                 flag = 0;
132             }
133             else
134             {
135                 temp = (str1[len1 - 1] - ‘0‘) + 10 - (str2[len2 - 1] - ‘0‘);
136                 flag = 1;
137             }
138             value[i++] = (char)(temp+(int)‘0‘);
139             len1--;
140             len2--;
141             if (len1 > 0 && len2 <= 0)
142             {
143                 len2 = 1;
144                 str2[0] = ‘0‘;
145             }
146         }
147     }
148     else if (str1<str2)//(Case==2)//情况二 小减大
149     {
150         value = (char *)malloc(len2*sizeof(char));
151         int temp;
152         while (len1 > 0 && len2 > 0)
153         {
154             if (flag == 1)//借位处理
155             {
156                 if (str2[len2 - 1] == ‘0‘)
157                 {
158                     str2[len2 - 1] = ‘9‘;
159                     flag = 1;
160                 }
161                 else if (str2[len2 - 1] != ‘0‘)
162                 {
163                     str2[len2 - 1] = str2[len2 - 1] - 1;
164                     flag = 0;
165                 }
166             }
167             if (str2[len2 - 1] >= str1[len1 - 1])
168             {
169                 temp = str2[len2 - 1] -str1[len1 - 1];
170                 flag = 0;
171             }
172             else
173             {
174                 temp = str2[len2 - 1] + 10 - str1[len1 - 1];
175                 flag = 1;
176             }
177             value[i++] = (char)(temp + (int)‘0‘);
178             len1--;
179             len2--;
180             if (len1 <= 0 && len2 > 0)
181             {
182                 len1 = 1;
183                 str1[0] = ‘0‘;
184             }
185         }
186         cout << "-";
187     }
188 
189     value[i] = ‘\0‘;
190     i--;
191     while (i >= 0 && value[i] == ‘0‘)
192     {
193         i--;
194     }
195     if (i < 0)
196     {
197         cout << 0;
198     }
199     else
200     {
201         for(; i >= 0; i--)
202         {
203             cout << value[i];
204         }
205     }
206 }
207 int main(void)
208 {
209     string str1,str2,result;
210     cin >> str1>>str2;
211     BDplus(str1, str2);
212     BDminus(str1, str2);
213 
214     return 0;
215 }