http://blog.csdn.net/hackbuteer1/article/details/6595881
#include<iostream> #include<string> #include<iomanip> #include<algorithm> using namespace std; #define MAXN 9999 #define MAXSIZE 10 #define DLEN 4 class BigNum { private: int a[500]; //可以控制大数的位数 int len; //大数长度 public: BigNum(){ len = 1; memset(a, 0, sizeof(a)); } //构造函数 BigNum(const int); //将一个int类型的变量转化为大数 BigNum(const char*); //将一个字符串类型的变量转化为大数 BigNum(const BigNum &); //拷贝构造函数 BigNum &operator=(const BigNum &); //重载赋值运算符，大数之间进行赋值运算 friend istream& operator>>(istream&, BigNum&); //重载输入运算符 friend ostream& operator<<(ostream&, BigNum&); //重载输出运算符 BigNum operator+(const BigNum &) const; //重载加法运算符，两个大数之间的相加运算 BigNum operator-(const BigNum &) const; //重载减法运算符，两个大数之间的相减运算 BigNum operator*(const BigNum &) const; //重载乘法运算符，两个大数之间的相乘运算 BigNum operator/(const int &) const; //重载除法运算符，大数对一个整数进行相除运算 BigNum operator^(const int &) const; //大数的n次方运算 int operator%(const int &) const; //大数对一个int类型的变量进行取模运算 bool operator>(const BigNum & T)const; //大数和另一个大数的大小比较 bool operator>(const int & t)const; //大数和一个int类型的变量的大小比较 void print(); //输出大数 }; BigNum::BigNum(const int b) //将一个int类型的变量转化为大数 { int c, d = b; len = 0; memset(a, 0, sizeof(a)); while (d > MAXN) { c = d - (d / (MAXN + 1)) * (MAXN + 1); d = d / (MAXN + 1); a[len++] = c; } a[len++] = d; } BigNum::BigNum(const char*s) //将一个字符串类型的变量转化为大数 { int t, k, index, l, i; memset(a, 0, sizeof(a)); l = strlen(s); len = l / DLEN; if (l%DLEN) len++; index = 0; for (i = l - 1; i >= 0; i -= DLEN) { t = 0; k = i - DLEN + 1; if (k<0) k = 0; for (int j = k; j <= i; j++) t = t * 10 + s[j] - '0'; a[index++] = t; } } BigNum::BigNum(const BigNum & T) : len(T.len) //拷贝构造函数 { int i; memset(a, 0, sizeof(a)); for (i = 0; i < len; i++) a[i] = T.a[i]; } BigNum & BigNum::operator=(const BigNum & n) //重载赋值运算符，大数之间进行赋值运算 { int i; len = n.len; memset(a, 0, sizeof(a)); for (i = 0; i < len; i++) a[i] = n.a[i]; return *this; } istream& operator>>(istream & in, BigNum & b) //重载输入运算符 { char ch[MAXSIZE * 4]; int i = -1; in >> ch; int l = strlen(ch); int count = 0, sum = 0; for (i = l - 1; i >= 0;) { sum = 0; int t = 1; for (int j = 0; j<4 && i >= 0; j++, i--, t *= 10) { sum += (ch[i] - '0')*t; } b.a[count] = sum; count++; } b.len = count++; return in; } ostream& operator<<(ostream& out, BigNum& b) //重载输出运算符 { int i; cout << b.a[b.len - 1]; for (i = b.len - 2; i >= 0; i--) { cout.width(DLEN); cout.fill('0'); cout << b.a[i]; } return out; } BigNum BigNum::operator+(const BigNum & T) const //两个大数之间的相加运算 { BigNum t(*this); int i, big; //位数 big = T.len > len ? T.len : len; for (i = 0; i < big; i++) { t.a[i] += T.a[i]; if (t.a[i] > MAXN) { t.a[i + 1]++; t.a[i] -= MAXN + 1; } } if (t.a[big] != 0) t.len = big + 1; else t.len = big; return t; } BigNum BigNum::operator-(const BigNum & T) const //两个大数之间的相减运算 { int i, j, big; bool flag; BigNum t1, t2; if (*this>T) { t1 = *this; t2 = T; flag = 0; } else { t1 = T; t2 = *this; flag = 1; } big = t1.len; for (i = 0; i < big; i++) { if (t1.a[i] < t2.a[i]) { j = i + 1; while (t1.a[j] == 0) j++; t1.a[j--]--; while (j > i) t1.a[j--] += MAXN; t1.a[i] += MAXN + 1 - t2.a[i]; } else t1.a[i] -= t2.a[i]; } t1.len = big; while (t1.a[t1.len - 1] == 0 && t1.len > 1) { t1.len--; big--; } if (flag) t1.a[big - 1] = 0 - t1.a[big - 1]; return t1; } BigNum BigNum::operator*(const BigNum & T) const //两个大数之间的相乘运算 { BigNum ret; int i, j, up; int temp, temp1; for (i = 0; i < len; i++) { up = 0; for (j = 0; j < T.len; j++) { temp = a[i] * T.a[j] + ret.a[i + j] + up; if (temp > MAXN) { temp1 = temp - temp / (MAXN + 1) * (MAXN + 1); up = temp / (MAXN + 1); ret.a[i + j] = temp1; } else { up = 0; ret.a[i + j] = temp; } } if (up != 0) ret.a[i + j] = up; } ret.len = i + j; while (ret.a[ret.len - 1] == 0 && ret.len > 1) ret.len--; return ret; } BigNum BigNum::operator/(const int & b) const //大数对一个整数进行相除运算 { BigNum ret; int i, down = 0; for (i = len - 1; i >= 0; i--) { ret.a[i] = (a[i] + down * (MAXN + 1)) / b; down = a[i] + down * (MAXN + 1) - ret.a[i] * b; } ret.len = len; while (ret.a[ret.len - 1] == 0 && ret.len > 1) ret.len--; return ret; } int BigNum::operator %(const int & b) const //大数对一个int类型的变量进行取模运算 { int i, d = 0; for (i = len - 1; i >= 0; i--) { d = ((d * (MAXN + 1)) % b + a[i]) % b; } return d; } BigNum BigNum::operator^(const int & n) const //大数的n次方运算 { BigNum t, ret(1); int i; if (n<0) exit(-1); if (n == 0) return 1; if (n == 1) return *this; int m = n; while (m>1) { t = *this; for (i = 1; i << 1 <= m; i <<= 1) { t = t*t; } m -= i; ret = ret*t; if (m == 1) ret = ret*(*this); } return ret; } bool BigNum::operator>(const BigNum & T) const //大数和另一个大数的大小比较 { int ln; if (len > T.len) return true; else if (len == T.len) { ln = len - 1; while (a[ln] == T.a[ln] && ln >= 0) ln--; if (ln >= 0 && a[ln] > T.a[ln]) return true; else return false; } else return false; } bool BigNum::operator >(const int & t) const //大数和一个int类型的变量的大小比较 { BigNum b(t); return *this>b; } void BigNum::print() //输出大数 { int i; cout << a[len - 1]; for (i = len - 2; i >= 0; i--) { cout.width(DLEN); cout.fill('0'); cout << a[i]; } cout << endl; } int main(void) { BigNum x(1234567890); BigNum y(x); cout << x + y << endl; cout << x - y << endl; cout << x * y << endl; }