create numbers with strings

Question

0.00/5 (No votes)

See more:

I am trying to create a class to calculate Big Numbers with strings.
The Add method isn't working. I think the logic is wrong. Any suggestions how to fix this? Thanks in advance.

C++

#include "NumberString.h"


NumberString::NumberString()
{
	this->_number = "0";
}

NumberString::NumberString(string s)
{
	this->_number = s;
}

NumberString::~NumberString()
{
}

void NumberString::Add(string number)
{
	string top = this->_number;
	string bottom = number;
	if (number.size() > top.size())
	{
		top = number;
		bottom = _number;
	}
	string sum;
	char t=0, b=0, l=0, c='0';
	size_t n = top.size();
	size_t m = bottom.size();
	for (size_t i = 0; i < n; i++)
	{
		t = top.at(n - i - 1);
		if (c != '0')
		{
			this->AddChars(t, c, &l, &c);
		}

		if (i < m)
		{
			b = bottom.at(m - i - 1);
			this->AddChars(t, b, &l, &c);
		}

		sum.insert(0, 1, l);		
	}

	if (c != '0')
	{
		sum.insert(0, 1, c);
	}

	this->_number = sum;
}

void NumberString::AddChars(char first, char second, char *last, char* carry)
{
	*carry = '0';
	char c = first + second - '0';
	if (c > '9')
	{
		*carry = '1';
		c -= 10;
	}
	*last = c;
}

void NumberString::Multiply(uint64_t number)
{
	NumberString n = this->_number;
	if (number == 0)
	{
		this->_number = "0";
		return;
	}
	else if (number == 1)
		return;

	for (uint64_t i = 0; i < number-1; i++)
	{
		this->Add(n);
	}
}

void NumberString::Print()
{
	cout << this->_number.c_str() << endl;
}

string NumberString::GetNumber()
{
	return this->_number;
}

void NumberString::Add(NumberString number)
{
	this->Add(number._number);
}

Posted 31-Mar-15 1:42am

BacchusBeale

Add a Solution

Comments

OriginalGriff 31-Mar-15 8:11am

"isn't working. I think the logic is wrong"
That isn't very helpful - remember that we can't see your screen, access your HDD, or read your mind.
So tell us what you did to get results, tell us what that did do that you didn't expect, or did do that you didn't! Tell us if there are error messages, bad numbers, poor results. Give us information to help us help you!
Use the "Improve question" widget to edit your question and provide better information.

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

CPallini · Accepted Answer · 2015-03-31T02:55:00

Your code doesn't properly propagate the carry that may occur here

Quote:
if (c != '0')
{
this->AddChars(t, c, &l, &c);
}

Moreover, it incorrectly always sums t with b (it should sum l with b when carry occurs).

In order to avoid cumbersome carry propagation, I would suggest to define

C++

char NumberString::AddCharsWithCarry( char first, char second, char & carry)
{
  char r = first - '0' + second - '0' + carry;
  if ( r > '9')
  {
    r -= 10;
    carry = '1';
  }
  else
  {
    carry = '0';
  }
  return r;
}

This method sums first, second and carry, returning the result (and updating the carry parameter). This way the loop inside your Add method would become very simple:

C++

for (size_t i = 0; i < n; i++)
{
  t = top.at(n - i - 1);
  b = i < m ? bottom.at(m -i -1) : '0';
  l = AddCharsWithCarry(t, b, c);

  sum.insert(0, 1, l);
}