C++ std::list实现大整数加法运算

#pragma once #include <iostream> #include <list> #include <string> using namespace std; class CBigInt { public: CBigInt(void); CBigInt(const string& _str); CBigInt& Set(const string& _str); ~CBigInt(void); friend std::ostream& operator<<(std::ostream& os, const CBigInt& _bigInt); friend std::istream& operator>>(std::istream& is, CBigInt& _bigInt); friend CBigInt operator+(const CBigInt& lhs, const CBigInt& rhs); friend CBigInt operator-(const CBigInt& lhs, const CBigInt& rhs); private: static short add(short& carry, const short a=0, const short b=0); private: std::list<short> m_list; };

 

 

#include "BigInt.h" #include <string> #include <streambuf> #include <iterator> CBigInt::CBigInt(void) { } CBigInt::CBigInt(const string& _str) { for (auto itr = _str.cbegin(); itr != _str.cend(); ++itr) { m_list.push_back(*itr-'0'); } } CBigInt& CBigInt::Set(const string& _str) { m_list.clear(); for (auto itr = _str.cbegin(); itr != _str.cend(); ++itr) { m_list.push_back(*itr-'0'); } return *this; } CBigInt::~CBigInt(void) { } std::ostream& operator<<(std::ostream& os, const CBigInt& _bigInt) { for (auto itr = _bigInt.m_list.cbegin(); itr != _bigInt.m_list.cend(); ++itr) { os<<*itr; } return os; } std::istream& operator>>(std::istream& is, CBigInt& _bigInt) { std::string str; std::getline(is, str); for (std::size_t i = 0; i< str.length(); ++i) { short s = str[i]-'0'; _bigInt.m_list.push_back(s); } return is; } short CBigInt::add(short& carry, const short a, const short b) { short current = (a + b + carry); carry = (a + b + carry)/10; return current; } CBigInt operator+(const CBigInt& lhs, const CBigInt& rhs) { //如果长度不同，可以补0，那种方式比较好算,但是开辟的内存较多，不划算 CBigInt retBinInt; short carry = 0; auto itrLhs = lhs.m_list.crbegin(), itrRhs = rhs.m_list.crbegin(); for ( ;itrLhs != lhs.m_list.crend() && itrRhs != rhs.m_list.crend(); ++itrLhs, ++itrRhs) { retBinInt.m_list.push_front(CBigInt::add(carry, *itrLhs, *itrRhs)); } if (itrLhs != lhs.m_list.crend()) { for (; itrLhs != lhs.m_list.crend(); ++itrLhs) { retBinInt.m_list.push_front(CBigInt::add(carry, *itrLhs)); } } if (itrRhs != rhs.m_list.crend()) { for (; itrRhs != rhs.m_list.crend(); ++itrRhs) { retBinInt.m_list.push_front(CBigInt::add(carry, *itrRhs)); } } if (carry !=0) { retBinInt.m_list.push_front(1); } return retBinInt; } CBigInt operator-(const CBigInt& lhs, const CBigInt& rhs) { return CBigInt(); }

 

 

#include <iostream> using namespace std; #include <vector> #include <utility> #include "BigInt.h" void AddTest(const std::string& _a, const std::string& _b) { CBigInt a,b; cout<<"a="<<a.Set(_a)<<" "; cout<<"b="<<b.Set(_b)<<endl; cout<<"a+b="<<a+b<<endl; } int main(int , char**) { AddTest("2", "3"); AddTest("22", "333"); AddTest("66", "777"); AddTest("777", "666"); AddTest("999", "1"); AddTest("1", "999"); AddTest("999908", "92"); AddTest("123456789", "987654321"); AddTest("999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999908" , "92"); std::cout<<"please input a,b:\n"; CBigInt a,b; std::cin>>a>>b; cout<<"a+b=\n"<<a+b<<endl; return 0; }