就一个简单的大数计算

也只是刚刚写出了加法，用的是1 000 000 000进制，不过发现对于加法还不如用最基本的方法方便。用1 000 000 000进制的方便也就在于处理乘法和除法了。计算机做乘除运算还是比较耗时的。

#include <random>
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <utility>
using namespace std;
const int MaxNum=1000000000; //进制
class BigNumCalcu{
public:
    const static int N=9;
    BigNumCalcu():num_1(""),result(""),numSize_1(0),numSize_2(0){  //init
        num_2="";
    fopen.open("num.txt");
    }
    string patchZero(int M); //补0
  void getInput();   //读取数据
  void SplitNum(); 
  void Sum();      //加法
  string Sub();      //减法
  void Multi();    //乘法
  string Div();      //除法
  void randomData();
private:
  fstream fopen;
  vector<int> BitNum_1,BitNum_2;
  string num_1,num_2,result;
  unsigned int numSize_1;
  unsigned int numSize_2;
};

void BigNumCalcu::getInput(){
  for(int i=0;i!=5;++i){
    result="";
    BitNum_1.clear();
    BitNum_2.clear();
    fopen>>num_1>>num_2;
    cout<<"num_1: "<<num_1<<" num_2: "<<num_2<<endl;
    SplitNum();
    Sum();
  }
}
void BigNumCalcu::SplitNum(){
  numSize_1=(num_1.size()%9==0) ? num_1.size()/9 : num_1.size()/9+1;
  numSize_2=(num_2.size()%9==0) ? num_2.size()/9 : num_2.size()/9+1;
  //split
  if(numSize_1==num_1.size()/9)
    for(int index=1;index<=numSize_1;++index)
      BitNum_1.push_back(std::stoi(num_1.substr(num_1.size()-index*BigNumCalcu::N,9)));
  else
    for(int index=1;index<=numSize_1;++index){
      if(index==numSize_1)
    BitNum_1.push_back(std::stoi(num_1.substr(0,num_1.size()-(index-1)*BigNumCalcu::N)));
      else
    BitNum_1.push_back(std::stoi(num_1.substr(num_1.size()-index*BigNumCalcu::N,9)));        
    }

  if(numSize_2==num_2.size()/9)
    for(int index=1;index<=numSize_2;++index)
      BitNum_2.push_back(std::stoi(num_2.substr(num_2.size()-index*BigNumCalcu::N,9)));
  else
    for(int index=1;index<=numSize_2;++index){
      if(index==numSize_2)
    BitNum_2.push_back(std::stoi(num_2.substr(0,num_2.size()-(index-1)*BigNumCalcu::N)));
      else
    BitNum_2.push_back(std::stoi(num_2.substr(num_2.size()-index*BigNumCalcu::N,9)));        
    }
}

string BigNumCalcu::patchZero(int M){
  auto it=std::to_string(M).size();
  string temp=std::to_string(M);

  if(it<BigNumCalcu::N){
    for(;it<BigNumCalcu::N;it++)
      temp="0"+temp;
    return result=temp+result;
  }
  else
    return result=std::to_string(M);
}

void BigNumCalcu::Sum(){
  int min=std::min(numSize_1,numSize_2);
  int index=0;  //进位
  int sum=0;
  //如果兩個數字具有相同的位数



  //如果两个数字位数不一样
  if(min==numSize_1)
    for(int count=min;count<numSize_2;++count)
      if((sum=BitNum_2[count]+index)>=MaxNum){
    index=1;
    result=patchZero(sum-MaxNum);
      }
      else{
    index=0;
    result=patchZero(sum);
      }
  else
    for(int count=min;count<numSize_1;++count)
      if((sum=BitNum_1[count]+index)>=MaxNum){
    index=1;
    result=patchZero(sum-MaxNum);
      }
      else{
    index=0;
    result=patchZero(sum);
      }

  //如果最高位也需要进位
  if(index==1)
    result="1"+result;
  cout<<result<<endl;
}

int main(int argc,char **argv){
  BigNumCalcu Calc;
  Calc.getInput();
  return 0;
}

下面是一个python测试。因为python已经自带大整数计算了

__author__='MarkLiang'
#coding=utf-8

fopen=open('num.txt','r')
for num1 in fopen:
    num2=fopen.readline();
    print("result: ",int(num1)+int(num2))

fopen.close()

至于乘法和除法，我有空在写吧。