new to C++ and I don't understand what it means...

Aaronugio · 07-20-2009, 10:00 AM

Working in VC++ and here's my problem, was reading through my "SAMS Teach yourself C++ in 1 hour a day" and got to chapter 13 which is supposed to teach operator overloading, but when I modified the code from the book, as such:

Code:

#include <iostream>

using namespace std;

class number //class to test the reprogramming of the "++" increment operator
{
public:
	number();
	~number();
	int mynumber;
	
	void inc(int increment) // replacement function for ++ operator
	{
		mynumber += increment;
	}

	number& operator ++ () // reprogramming the ++ operator
	{
		inc(1);
		return *this;
	}
	void dmn() // dmn = display mynumber
	{
		cout << mynumber;
	}
	void setnum(int x)// sets mynumber value
	{
		mynumber = x;
	}
};

int main()
{
	int z;
	cout << "Please choose start point : ";
	cin >> z;

	number newnumb();
	newnumb.setnum(z);
	newnumb.dmn();
	++ newnumb;
	newnumb.dmn();
	system("PAUSE");
	return 0;
}

it gives me the errors:

1. error C2228: left of '.setnum' must have class/struct/union
2. error C2228: left of '.dmn' must have class/struct/union
3. error C2171: '++' : illegal on operands of type 'number (__cdecl *)(void)'
4. error C2105: '++' needs l-value
5. warning C4550: expression evaluates to a function which is missing an argument list
6. error C2228: left of '.dmn' must have class/struct/union

1, 2, and 6 annoy me, because I don't understand why it's printing it
3 and 4, I am just clueless as to what they mean...

tabstop · 07-20-2009, 10:03 AM

You know what () means -- it means function call.

This:

Code:

number newnumb;

is a declaration of a number object. This:

Code:

number newnumb();

is a declaration of a function that returns a number object.

Aaronugio · 07-20-2009, 10:10 AM

Thanks but that has lead me to another problem, when I changed it, it gave me these errors...

: error LNK2019: unresolved external symbol "public: __thiscall number::~number(void)" (??1number@@QAE@XZ) referenced in function _main
1>main.obj : error LNK2019: unresolved external symbol "public: __thiscall number::number(void)" (??0number@@QAE@XZ) referenced in function _main

do I need to manually call on the constructor and destructor?

bithub · 07-20-2009, 10:12 AM

You have declared a destructor, but there is no implementation.

Code:

~number();

Where is the code for ~number()?

EDIT: Also, the code for your constructor is missing too.

anon · 07-20-2009, 10:15 AM

You have declared but not defined the constructor and destructor. (You can probably just remove the destructor declaration, and your constructor should probably set the number to some value - like 0, or do what setnum does.)

Aaronugio · 07-20-2009, 10:20 AM

Thanks you guys I'm sorry if this seemed very wasteful of your time, but thanks for helping me, I've only been seriously trying to learn for about 2 weeks now, but sometimes i just forget parts.

I'm gonna take your suggestion and see if I can remove the destructor and write in a value-setting function within the constructor.

thanks again.

Aaronugio · 07-20-2009, 10:23 AM

it worked thanks again so much

**Salem** · 07-20-2009, 10:24 AM

> SAMS Teach yourself C++ in 1 hour a day
Should be "SAMS Teach yourself to tell the difference between C++ and a hole in the ground in 1 hour a day"

07-20-2009, 10:00 AM	#1
Aaronugio Registered User Join Date: Jul 2009 Posts: 14	new to C++ and I don't understand what it means... Working in VC++ and here's my problem, was reading through my "SAMS Teach yourself C++ in 1 hour a day" and got to chapter 13 which is supposed to teach operator overloading, but when I modified the code from the book, as such: Code: #include <iostream> using namespace std; class number //class to test the reprogramming of the "++" increment operator { public: number(); ~number(); int mynumber; void inc(int increment) // replacement function for ++ operator { mynumber += increment; } number& operator ++ () // reprogramming the ++ operator { inc(1); return this; } void dmn() // dmn = display mynumber { cout << mynumber; } void setnum(int x)// sets mynumber value { mynumber = x; } }; int main() { int z; cout << "Please choose start point : "; cin >> z; number newnumb(); newnumb.setnum(z); newnumb.dmn(); ++ newnumb; newnumb.dmn(); system("PAUSE"); return 0; } it gives me the errors: 1. error C2228: left of '.setnum' must have class/struct/union 2. error C2228: left of '.dmn' must have class/struct/union 3. error C2171: '++' : illegal on operands of type 'number (__cdecl )(void)' 4. error C2105: '++' needs l-value 5. warning C4550: expression evaluates to a function which is missing an argument list 6. error C2228: left of '.dmn' must have class/struct/union 1, 2, and 6 annoy me, because I don't understand why it's printing it 3 and 4, I am just clueless as to what they mean...
Aaronugio is offline

07-20-2009, 10:03 AM	#2
tabstop and the Hat of Guessing Join Date: Nov 2007 Posts: 8,740	You know what () means -- it means function call. This: Code: number newnumb; is a declaration of a number object. This: Code: number newnumb(); is a declaration of a function that returns a number object.
tabstop is offline

07-20-2009, 10:10 AM	#3
Aaronugio Registered User Join Date: Jul 2009 Posts: 14	Thanks but that has lead me to another problem, when I changed it, it gave me these errors... : error LNK2019: unresolved external symbol "public: __thiscall number::~number(void)" (??1number@@QAE@XZ) referenced in function _main 1>main.obj : error LNK2019: unresolved external symbol "public: __thiscall number::number(void)" (??0number@@QAE@XZ) referenced in function _main do I need to manually call on the constructor and destructor? Last edited by Aaronugio; 07-20-2009 at 10:14 AM.
Aaronugio is offline

07-20-2009, 10:12 AM	#4
bithub Registered User Join Date: Sep 2004 Location: California Posts: 2,845	You have declared a destructor, but there is no implementation. Code: ~number(); Where is the code for ~number()? EDIT: Also, the code for your constructor is missing too.
bithub is offline

07-20-2009, 10:20 AM	#6
Aaronugio Registered User Join Date: Jul 2009 Posts: 14	Thanks Thanks you guys I'm sorry if this seemed very wasteful of your time, but thanks for helping me, I've only been seriously trying to learn for about 2 weeks now, but sometimes i just forget parts. I'm gonna take your suggestion and see if I can remove the destructor and write in a value-setting function within the constructor. thanks again.
Aaronugio is offline

07-20-2009, 10:23 AM	#7
Aaronugio Registered User Join Date: Jul 2009 Posts: 14	it worked thanks again so much
Aaronugio is offline

07-20-2009, 10:24 AM	#8
Salem and the hat of vanishing Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,214	> SAMS Teach yourself C++ in 1 hour a day Should be "SAMS Teach yourself to tell the difference between C++ and a hole in the ground in 1 hour a day" __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut. Up to 8Mb PlusNet broadband from only £5.99 a month!
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