面试题之自创 大数相加减

大数相加减

这是我补前面大正整数相加减的博客，正数很常用，但是如果出现负数，我们肿么办？

#include <iostream>
#include <string>
using namespace std;

// extra the class of string
class String:public string
{
public:
// mode the add of int
static string ADD_Int(string a,string b)
{
// exception of input
if( a.empty() )
return b;
else if( b.empty() )
return "0";
if(!check_all_number(a) || !check_all_number(b))
{
return "exception of input ADD_Int";
}
Standardization(a);
Standardization(b);

if(a[0] != '-' && b[0] != '-')
return AddInt(a,b);
else if(a[0] != '-'&& b[0] == '-')
return MultipliesInt( a,b.substr( 1,b.size() ) );
else if(a[0] == '-'&& b[0] != '-')
return MultipliesInt(b,a.substr(1,a.size()));
else return '-'+AddInt(a.substr(1,a.size()),b.substr( 1,b.size() ));
}

// make a-b mode int a - b;
static string MUL_Int(string a,string b)
{
// exception of input
if( a.empty() )
return b;
else if( b.empty() )
return "0";
if(!check_all_number(a) || !check_all_number(b))
{
return "exception of input Multiplies_Int";
}
Standardization(a);
Standardization(b);
if(a[0] != '-' && b[0] != '-')
return MultipliesInt(a,b);
else if(a[0] != '-' && b[0] == '-')
return AddInt(a,b.substr(1,b.size()));
else if(a[0] == '-' && b[0] != '-')
return "-"+AddInt(a.substr(1,a.size()),b);
else return MultipliesInt( b.substr(1,b.size()) , a.substr(1,a.size()) );
}

private:

// make a-b mode int a - b;
static string MultipliesInt(string a,string b)
{
// exception of input
if(!check_all_number(a) || !check_all_number(b))
return "exception of input Multiplies";
Standardization(a);
Standardization(b);
// particular string of input
if(a.empty())
{
if(b.empty())
return "0";
else
return "-"+b;
}
else if(b.empty())
{
return a;
}

// normal number a < b
string c = "";
bool check = true ;
if(Compare(a,b) == '=')
return "0";
else if(Compare(a,b) == '<')
{
c = a ;
a = b ;
b = c ;
c = "";
check = false ;
}
// normal number a >= b
string::size_type i = a.size()-1, j = b.size()-1;
int jiewei = 0,now;

while(i < a.size() && j < b.size())
{
now = CharToNumber(a[i]) - CharToNumber(b[j]) - jiewei ;

if( now < 0 )
{
jiewei = 1;
now = 10 + now ;
}
else jiewei = 0;
c = IntToChar(now)  + c ;
i--;j--;
}
while(i < a.size())
{
now = CharToNumber(a[i]) - jiewei ;
if( now < 0 )
{
jiewei = 1;
now = 10 + now ;
}
else jiewei = 0;
c = IntToChar( now )  + c ;
i--;
}
Standardization(c);
if(!check)
c = '-' + c;
return c;
}

// mode the add of int
static string AddInt(string a,string b)
{
// exception of input
if( a.empty() )
return b;
else if( b.empty() )
return "0";
if(!check_all_number(a) || !check_all_number(b))
{
return "exception of input AddInt";
}
Standardization(a);
Standardization(b);
string::size_type i = a.size()-1 ,j = b.size()-1 , k = 0 ;
string c = "";
int jinwei = 0;
while( i < a.size() && j < b.size() )
{
c = IntToChar( ( CharToNumber(a[i]) + CharToNumber(b[j]) + jinwei ) % 10 ) + c;
jinwei = ( CharToNumber(a[i]) + CharToNumber(b[j]) + jinwei ) / 10;
j--;i--;
}
while( j < b.size()  )
{
c =  IntToChar( ( CharToNumber(b[j]) + jinwei ) % 10 ) + c;
jinwei = ( jinwei + CharToNumber(b[j]) ) / 10;
j--;
}
while( i < a.size() )
{
c =  IntToChar( ( CharToNumber(a[i]) + jinwei ) % 10 ) + c;
jinwei = ( jinwei + CharToNumber(a[i]) ) / 10;
i--;
}
if( jinwei )
c = IntToChar(  jinwei  ) + c;
return c;
}

// make char to the int number
static int CharToNumber(char c)
{
if( c >= '0' && c <= '9' )
return int(c - '0');
else
{
cout<<"exception of input CharToNumber "<<endl;
system("pause");
return 0;
}
}

// make int to the model char
static char IntToChar(int i)
{
if( i >= 0 && i <= 9 )
{
return char(i+48);
}
else
{
cout<<i<<" exception of input IntToChar"<<endl;
system("pause");
}
}

// check whether the string is legal
static bool check_all_number(string a)
{
if(a.empty())
return true ;
string::size_type L = a.size(),i = 0;
if(a[0] == '-')
i++;
while( i < L )
{
if( a[i] < '0' || a[i] > '9')
return false;
i++;
}
return true ;
}

// compare string a and b
static char Compare(string a,string b)
{
if(a.empty() || b.empty())
{
cout<<"error of imput compare";
return 'e';
}
else
{
if(a.size() > b.size())
return '>' ;
else if(a.size() == b.size())
{
for(string::size_type i = 0;i < a.size(); i++)
{
if(a[i] > b[i])
return '>';
if(a[i] < b[i])
return '<';
}
return '=';
}
return '<';
}
}

// make string into standard number
static void Standardization(string &a)
{
if(!check_all_number(a))
{
cout<<a<<" exception of input Standardization"<<endl;
}
string::size_type i = 0;
bool fushu = false ;
if( a[0] == '-' )
{
fushu = true;
i = 1;
}
while(i < a.size())
{
if(a[i] != '0')
break;
i++;
}
if(i == a.size())
i--;
a = a.substr(i,a.size());
if( fushu && a != "0")
a = '-' + a;
}
};

// main function
int main()
{
string a ;
string b ;
cin>>a>>b;
cout<<"a="<<a<<",b="<<b<<endl;
cout<<"add = "<<String::ADD_Int(a,b)<<endl;
cout<<"mul = "<<String::MUL_Int(a,b)<<endl;
system("pause");
return 0;
}