bignum 大数模板

　　今天无意间看到一个很好的大数模板，能算加、减、乘、除等基本运算，但操作减法的时候只能大数减小数，也不支持负数，如果是两个负数的话去掉符号相加之后再取反就可以了，一正一负比较绝对值大小，然后相减。我借用了一下：（作过少许代码上的精简）

  1 #include<cstdio> 

  2 #include<cstring>

  3 #include<string>

  4 #include<algorithm>

  5 #include<iostream>

  6 using namespace std;

  7 

  8 const int maxn = 2003;

  9 

 10 struct bign{

 11     int len, s[maxn];

 12     bign(){

 13         memset(s,0,sizeof(s));

 14         len= 1;

 15     }

 16     bign(int num)    {    *this = num;    }

 17     bign(const char *num)    {    *this = num;    }

 18     bign operator = (const int num){

 19         char s[maxn];

 20         sprintf(s,"%d",num);

 21         return *this = s;

 22     }

 23     bign operator = (const char *num){

 24         for(int i = 0; num[i] =='0'; ++num) ;

 25         len = strlen(num);

 26         for(int i = 0; i < len; ++i)

 27             s[i] = num[len-1-i] -'0';

 28         return *this;

 29     }

 30     bign operator + (const bign &b) const {

 31         bign c;

 32         c.len = 0;

 33         int maxlen = max(len, b.len);

 34         for(int i = 0, g = 0; g || i < maxlen; ++i){    // g是进位 

 35             int x = g;

 36             if(i < len)      x += s[i];

 37             if(i < b.len)    x += b.s[i];

 38             c.s[c.len++] = x % 10;

 39             g = x / 10;

 40         }

 41         return c;

 42     }

 43     bign operator += (const bign &b){

 44         return *this = *this + b;

 45     }

 46     void clean(){

 47         while(len >1 && !s[len-1])    --len;

 48     }

 49     bign operator * (const bign &b) const {

 50         bign c;

 51         c.len = len + b.len;

 52         

 53         for(int i = 0; i < len; ++i)

 54             for(int j = 0; j < b.len; ++j)

 55                 c.s[i+j] += s[i] * b.s[j];

 56                 

 57         for(int i = 0; i < c.len; ++i){

 58             c.s[i+1] += c.s[i]/10;

 59             c.s[i] %= 10;

 60         }

 61         c.clean();

 62         return c;

 63     }

 64     bign operator *= (const bign &b){

 65         return *this = *this * b;

 66     }

 67     bign operator -(const bign &b) const {

 68         bign c;

 69         c.len = 0;

 70         for(int i = 0, g = 0; i < len; ++i){    //此时的 g是退位

 71             int x = s[i]- g;

 72             if(i < b.len)    x -= b.s[i];

 73             if(x >= 0)    g = 0;

 74             else {

 75                 g = 1;

 76                 x += 10;

 77             }

 78             c.s[c.len++] = x;

 79         }

 80         c.clean();

 81         return c;

 82     }

 83     bign operator -= (const bign &b){

 84         return *this = *this - b;

 85     }

 86     bign operator / (const bign &b) const {

 87         bign c, f = 0;

 88         for(int i = len-1; i >= 0; --i){

 89             f *= 10;

 90             f.s[0] = s[i];

 91             while(f >= b){

 92                 f -= b;

 93                 ++c.s[i];

 94             }

 95         }

 96         c.len = len;

 97         c.clean();

 98         return c;

 99     }

100     bign operator /= (const bign &b){

101         return *this = *this / b;

102     }

103     bign operator % (const bign &b) const {

104         bign r = *this / b;

105         return *this- r*b;

106     }

107     bign operator %= (const bign &b){

108         return *this = *this % b;

109     }

110     bool operator < (const bign &b) const {

111         if(len != b.len)    return len < b.len;

112         for(int i= len-1; i>=0; --i)

113             if(s[i] != b.s[i])    return s[i] < b.s[i];

114         return 0;

115     }

116     bool operator > (const bign &b) const {

117         if(len != b.len)    return len > b.len;

118         for(int i = len-1; i >= 0; --i)

119             if(s[i] != b.s[i])    return s[i] > b.s[i];

120         return 0;

121     }

122     bool operator == (const bign &b) const {

123         return !(*this < b || *this > b);

124     }

125     bool operator != (const bign &b) const {

126         return !(*this == b);

127     }

128     bool operator <= (const bign &b) const {

129         return *this < b || *this == b;

130     }

131     bool operator >= (const bign &b) const {

132         return *this > b || *this == b;

133     }

134     string str() const {

135         string res = "";

136         for(int i = 0; i < len; ++i)

137             res = char(s[i]+'0') + res;        //这里一定不能掉乱 +的顺序！ 

138         return res;

139     }

140 };

141 

142 istream& operator >> (istream &in, bign &x){

143     string s;

144     in >> s;

145     x = s.c_str();

146     return in;

147 }

148 

149 ostream& operator << (ostream &out, const bign &x){

150     out << x.str();

151     return out;

152 }

153 

154 int main()

155 {

156     bign a,b,c,d,e,f,g;

157     while(cin>>a>>b)

158     {

159         a.clean();

160         b.clean();

161         c = a+b;

162         d = a-b;

163         e = a*b;

164         f = a/b;

165         g = a%b;

166         cout<<"a+b = "<<c<<endl;

167         cout<<"a-b = "<<d<<endl;

168         cout<<"a*b = "<<e<<endl;

169         cout<<"a/b = "<<f<<endl;

170         cout<<"a%b = "<<g<<endl;

171         cout<<(a==b? "a = b":"a != b")<<endl;

172     }

173     return 0;

174 }

View Code

　　在此感谢原博客的模板提供： bign类C++高精度模板