Changing from positive to negative numbers

**vopo** · 08-07-2008

Hi,

I'm having some trouble trying to convert integer values from positive to negative and vice versa.

Here's an example of what I mean:
= 10 convert to -10
= -10 conver to 10

Here's my code:

Code:

#include "Number.h"

#include <iostream>
using std::cout;

int main()
{
	Number num;

	num.setNum(7);

	cout << "Number: is " << num.getNum() << "\n";

	return 0;
}

Code:

#ifndef NUMBER_H
#define NUMBER_H

class Number
{
public:
	Number();
	void setNum(const int &n);
	int getNum();
	int negation(int value);
private:
	int num;
};

#endif

Code:

#include "Number.h"


Number::Number()
{
	this->num = num;
}

void Number::setNum(const int &n)
{
	this->num = negation(n);
}

int Number::getNum()
{
	return num;
}

int Number::negation(int value)
{
	if(value < 0)
	{
		value  > value;
	}

	if(value > 0)
	{
		value < value;
	}

	return value;
}

**matsp** · 08-07-2008

Code:

int Number::negation(int value)
{
	if(value < 0)
	{
		value  > value;
	}

	if(value > 0)
	{
		value < value;
	}

	return value;
}

The red pieces above do not do anything useful [if the compiler doesn't completely optimize it away, it will generate a value of 0 since value < value and value > value are always false]. You should get some sort of warning from the compiler about "statement with no effect" if you enable warnings.

In math, how you do convert a value from positive to negative?

--
Mats

**vopo** · 08-07-2008

O ya, the compiler does give a warning.

I get it now how to convert from positive to negative:

-to get -10 from 10, I would need to do this:
0 - 10 = 10

Thanks for the help

**QuantumPete** · 08-07-2008

Originally Posted by vopo

-to get -10 from 10, I would need to do this:
0 - 10 = 10

Well, no, 0 - 10 = -10
Though, if you subtracted the number from 0, you would indeed get the right result. Normally though, you would multiply by -1 to switch between +ve and -ve.

QuantumPete

**matsp** · 08-07-2008

And if you have 10, and you want to make it negative [using a pen and paper], what do you do [and don't say "write 0-10=-10", but think of another, simpler solution].

--
Mats

**matsp** · 08-07-2008

[QUOTE=Elysia;778325]You can also use the negation operator:
[deleted]/QUOTE]

You spoilsport. I was trying to get the original poster to get there him/herself.
Edit: Now corrected.

--
Mats

**Elysia** · 08-07-2008

Originally Posted by matsp

You spoilsport. I was trying to get the original poster to get there him/herself.

--
Mats

I never posted anything

**Saimadhav** · 08-08-2008

try this simple and short code instead

Code:

#include<iostream.h>
#include<conio.h>
main()
{
      system("cls");
      int a,b;
      cout<<"Enter a number "<<endl;
      cin>>a;
      b=a-(2*a);
      cout<<"The interchanged value is "<<b;
      getch();
      return 0;
      }

**Elysia** · 08-08-2008

Implicit main is not allowed in C++.
Iostream.h is not a standard header.
cout, cin, endl are located in the std namespace.
conio.h is a non-standard header and getch() is a non-standard function. Better use cin.get() instead, and get rid of both those two.

Are by chance using Turbo C++ or some other old compiler? This won't compile.

**manzoor** · 08-08-2008

In Simple algebra

x * -1 = -x
-x * -1 = x

**matsp** · 08-08-2008

Originally Posted by manzoor

In Simple algebra

x * -1 = -x
-x * -1 = x

There is a simpler form tho'.

--
Mats

**QuantumPete** · 08-08-2008

Originally Posted by matsp

There is a simpler form tho'.

--
Mats

Ooh, bit-wise negation

QuantumPete

**matsp** · 08-08-2008

Originally Posted by QuantumPete

Ooh, bit-wise negation

QuantumPete

No, simpler than that [and in two's complement, it's bitwise negation + 1 - I don't know of ANY current machine using ones complement]

--
Mats

**m37h0d** · 08-08-2008

x*=-1;

**matsp** · 08-08-2008

Originally Posted by m37h0d

x*=-1;

There's a simpler answer. Just a basic assignment.

--
Mats

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