C++课程设计之大整数类 - c++编程基础

偶然间发现去年写的课程设计作业，写的还不错，涉及的知识面还挺多的，现在都有些记不得了，有时间得好好看看c++了。

题目: 设计并实现大整数类，并测试其加减乘除运算（至少有一个数是20位以上的整数）。利用它计算并显示30！。(要求：必须实现拷贝构造函数、四则运算重载、友元函数、插入和提取运算符重载)

问题分析：

要想实现真正的大整数类，即其位数不确定且可以无限大，那么选择容器是最佳的，用数组的话必须确定其大小，那么这个所谓的大整数的位数就有了上限，所以这里我选择用vector，并使用string类对其进行输入输出操作，代码如下。实现了拷贝构造函数、四则运算重载、友元函数、插入和提取运算符重载。四则运算对于负数也是适用的，除法只考虑求商。

代码实现：（运行环境为Microsoft Visual Studio 2010）

#include
  
   
#include
   
     #include
    
      #include
     
       using namespace std; class BigInt { public: BigInt(); BigInt(long int s); BigInt(string str); BigInt(BigInt& a); friend BigInt operator+(BigInt a,BigInt b); friend BigInt operator-(BigInt a,BigInt b); friend BigInt operator*(BigInt a,BigInt b); friend BigInt operator/(BigInt a,BigInt b);//除法算法不太好 friend ostream& operator<<(ostream& out,BigInt& a); friend istream& operator>>(istream& in,BigInt& a); BigInt operator=(BigInt a); friend int SizeJudge(BigInt a,BigInt b); vector
      
        vec; int negative;//0为正，1为负 }; BigInt::BigInt() { vec.push_back(0); negative = 0; } BigInt::BigInt(long int s) { if(s<0) { negative = 1; s = -s; } else negative = 0; int i; while(s>9) { i = s%10; vec.push_back(i); s /=10; } vec.push_back(s); } BigInt::BigInt(string str) { if(str[0] == '-') { negative = 1; str = str.substr(1,str.size()-1); } else negative = 0; for(int i=str.size()-1;i>=0;i--) { vec.push_back(str[i]-'0'); } } BigInt::BigInt(BigInt& a) { vec = a.vec; negative = a.negative; } BigInt BigInt::operator=(BigInt a) { vec = a.vec; negative = a.negative; return *this; } ostream& operator<<(ostream& out,BigInt& a) { string str=""; int judge = 0; if((a.vec[a.vec.size()-1]+'0') == '-') judge = 1; if((a.negative == 1)&&judge == 0) { str += '-'; } for(int i=a.vec.size()-1;i>=0;i--) { str += (a.vec[i]+'0'); } out<
       
        >(istream& in,BigInt& a) { string str=""; in>>str; a.vec.clear(); for(int i=str.size()-1;i>=0;i--) { a.vec.push_back(str[i]-'0'); } return in; } BigInt operator+(BigInt a,BigInt b) { int negative_judge = 0; if(a.negative == 1&&b.negative == 1)//全负 { negative_judge = 1; } if(a.negative == 0&&b.negative == 0)//全正 { negative_judge = 0; } if(a.negative == 0&&b.negative == 1)//a正b负 { b.negative = 0; return (a-b); } if(a.negative == 1&&b.negative == 0)//a负b正 { a.negative = 0; return (b-a); } BigInt c,tmp; int alen,blen,min,max,i; alen = a.vec.size(); blen = b.vec.size(); if(alen>blen) { c.vec = a.vec; tmp.vec = b.vec; min = blen; max = alen; } else { c.vec = b.vec; tmp.vec = a.vec; min = alen; max = blen; } for(i=0;i
        
         9) { c.vec[i] -= 10; c.vec[i+1] += 1; } } c.vec[i] +=tmp.vec[i]; if(c.vec[i]>9) { c.vec[i] -=10; if(min == max) c.vec.push_back(1); else c.vec[i+1] +=1; } for(i=min;i
         
          9) { c.vec[i] -=10; c.vec[i+1] +=1; } } if(c.vec[max-1]>9) { c.vec[max-1] -=10; c.vec.push_back(1); } i=c.vec.size()-1;//去掉前面的0 while(c.vec[i] == 0) { c.vec.pop_back(); i--; } if(negative_judge == 1) { string str = "-"; c.vec.push_back(str[0]-'0'); } return c; } BigInt operator-(BigInt a,BigInt b) { int negative_judge = 0; if(a.negative == 1&&b.negative == 1)//全负 { a.negative = 0; b.negative = 0; return (b-a); } if(a.negative == 0&&b.negative == 0)//全正 { negative_judge = 0; } if(a.negative == 0&&b.negative == 1)//a正b负 { b.negative = 0; return (a+b); } if(a.negative == 1&&b.negative == 0)//a负b正 { b.negative =1; return (a+b); } BigInt c,tmp; int alen,blen,min,max,i,judge=0; alen = a.vec.size(); blen = b.vec.size(); //大值赋给c，小值赋给tmp if(alen>blen) { c.vec = a.vec; tmp.vec = b.vec; min = blen; max = alen; judge = 1; } else if(alen == blen) { for(i=alen-1;i>=0;i--) { if(a.vec[i]>b.vec[i]) { c.vec = a.vec; tmp.vec = b.vec; min = blen; max = alen; judge = 1; break; } else if(a.vec[i]
          
           tmp { c.vec[i] -= tmp.vec[i]; if(c.vec[i]<0) { c.vec[i] += 10; c.vec[i+1] -= 1; } } if(min
           
            9) { if(i+j+1
            
             0) { j *=10; i--; } BigInt count(j); tmp = count*b; if(SizeJudge(a,tmp) == 1) { while(Siz

C++课程设计之大整数类(一)