UVa 10106 Product

　　大数加法，代码如下：
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  1 #include <cstdio>
  2 #include <iostream>
  3 #include <cstring>
  4 #include <algorithm>
  5 using namespace std;
  6 
  7 const int maxn = 1000;
  8 
  9 struct bign
 10 {
 11     int d[maxn];
 12     int len;
 13 
 14     bign()
 15     {
 16         memset(d, 0, sizeof(d));
 17         len = 1;
 18     }
 19 
 20     bign(int num)
 21     {
 22         *this = num;
 23     }
 24 
 25     bign(char * num)
 26     {
 27         *this = num;
 28     }
 29 
 30     bign operator = (const char * num)
 31     {
 32         len = strlen(num);
 33         for(int i = 0; i < len; i++)
 34             d[i] = num[len-1-i] - '0';
 35         return *this;
 36     }
 37 
 38     bign operator = (int num)
 39     {
 40         char s[maxn];
 41         sprintf(s, "%d", num);
 42         *this = s;
 43         return *this;
 44     }
 45 
 46     bign operator + (const bign& b) const
 47     {
 48         bign c;
 49         c.len = 0;
 50         int g = 0;
 51         for(int i = 0; i < max(len, b.len) || g; i++)
 52         {
 53             int x = g;
 54             if(i < len)   x += d[i];
 55             if(i < b.len)   x += b.d[i];
 56             c.d[c.len++] = x % 10;
 57             g = x / 10;
 58         }
 59         return c;
 60     }
 61 
 62     bign operator += (const bign& b)
 63     {
 64         *this = *this + b;
 65         return *this;
 66     }
 67 
 68     void clean()
 69     {
 70         while(len > 1 && !d[len-1])
 71             len--;
 72     }
 73     
 74     bign operator - (const bign& b)
 75     {
 76         bign c;
 77         c.len = 0;
 78         int g = 0;
 79         for(int i = 0; i < len; i++)
 80         {
 81             int x = d[i] - g;
 82             if(i < b.len)   x -= b.d[i];
 83             if(x >= 0)   g = 0;
 84             else 
 85             {
 86                 g = 1;
 87                 x += 10;
 88             }
 89             c.d[c.len++] = x;
 90         }
 91         c.clean();
 92         return c;
 93     }
 94 
 95     bign operator * (const bign& b)
 96     {
 97         bign c;
 98         c.len = len + b.len;
 99         for(int i = 0; i < len; i++)
100             for(int j = 0; j < b.len; j++)
101                 c.d[i+j] += d[i] * b.d[j];
102         for(int i = 0; i < c.len-1; i++)
103         {
104             c.d[i+1] += c.d[i] / 10;
105             c.d[i] %= 10;
106         }
107         c.clean();
108         return c;
109     }
110 
111     bool operator < (const bign& b) const
112     {
113         if(len != b.len)   return len < b.len;
114         for(int i = len-1; i >= 0; i--)
115             if(d[i] != b.d[i])   return d[i] < b.d[i];
116         return false;
117     }
118 
119     bool operator > (const bign& b) const
120     {
121         return b < *this;
122     }
123 
124     bool operator <= (const bign& b) const
125     {
126         return !(b < *this);
127     }
128 
129     bool operator >= (const bign& b) const
130     {
131         return !(*this < b);
132     }
133 
134     bool operator != (const bign& b) const
135     {
136         return b < *this || *this < b;
137     }
138 
139     bool operator == (const bign& b) const
140     {
141         return !(b < *this) && !(b > *this);
142     }
143 
144     string str() const
145     {
146         string res = "";
147         for(int i = 0; i < len; i++)
148             res = (char)(d[i]+'0') + res;
149         if(res == "")   res = "0";
150         return res;
151     }
152 };
153 
154 istream& operator >> (istream &in, bign& x)
155 {
156     string s;
157     in >> s;
158     x = s.c_str();
159     return in;
160 }
161 
162 ostream& operator << (ostream & out, const bign& x)
163 {
164     out << x.str();
165     return out;
166 }
167 
168 int main()
169 {
170 #ifdef LOCAL 
171     freopen("in", "r", stdin);
172 #endif
173     bign a, b;
174     while(cin>>a>>b)
175     {
176         bign c = a * b;
177         cout << c << endl;
178     }
179     return 0;
180 }
　　果然，有个模板就是好啊