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help with c++ classes

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help with c++ classes

Mar 18th, 2007

pls i will like you to help me with something
i was practising with c++ classes and i created a class interface called GradeBook, you know that i will need a source file to write the details of the implementation of the public functions? so in the source file i included the headeer file "GradeBook.h" then the next line i declared the class' constructor like this GradeBook::GradeBook(param goes here...){....} but the compiler returned an error message that a constructor cannot return a value, what pissed me off was that.... that's how it is written in the textbook i use; it must have been seeing the first GradeBook before the colons as a return type.. i am getting fed up..

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Re: help with c++ classes

Mar 18th, 2007

sometimes books contain errors. please post the code you are trying to compile so we can help you.

>>i am getting fed up
we all feel that way at times. But don't give up. When you feel really frustrated, walk away for awhile and do something else, like watch a good movie on TV.

Last edited by Ancient Dragon; Mar 18th, 2007 at 4:40 pm.

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Re: help with c++ classes

Mar 18th, 2007

//class GradeBook's source file

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
#include <iostream>
using std::cout;
using std::endl;
 
#include "GradeBook.h"// to tell the compiler i am using resources from class GradeBook
GradeBook::GradeBook(string name){
  setCourseName(name);
}
void GradeBook::setCourseName(string name){
 if(name.length() == 0){
  cout<<"\nName was not Entered";
 }
 if((name.length() > 0)&&(name.length() <=25)){
  courseName = name;
 }else 
  if(name.length()>25){
   courseName=name.substr(0,25);
   cout<<"\nName \""<<name<<"\" is more than 25 characters and has been truncated to 25"<<endl;
  }
}
string GradeBook::getCourseName(){
 return courseName;
}
void GradeBook::displayMessage(){
 
 cout<<"\nWelcome to the grade book of : "<<getCourseName()<<endl;
}
#include <iostream>
using std::cout;
using std::endl;

#include "GradeBook.h"// to tell the compiler i am using resources from class GradeBook
GradeBook::GradeBook(string name){
  setCourseName(name);
}
void GradeBook::setCourseName(string name){
 if(name.length() == 0){
  cout<<"\nName was not Entered";
 }
 if((name.length() > 0)&&(name.length() <=25)){
  courseName = name;
 }else 
  if(name.length()>25){
   courseName=name.substr(0,25);
   cout<<"\nName \""<<name<<"\" is more than 25 characters and has been truncated to 25"<<endl;
  }
}
string GradeBook::getCourseName(){
 return courseName;
}
void GradeBook::displayMessage(){
  
 cout<<"\nWelcome to the grade book of : "<<getCourseName()<<endl;
}

Last edited by Ancient Dragon; Mar 18th, 2007 at 4:51 pm. Reason: add code tags

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Re: help with c++ classes

Mar 18th, 2007

1. you did not include the header file <string>

2. If you are not declaring using namespace std: after the includes then you need to declare the namespace at each object instance. For example, line 6 would read

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GradeBook::GradeBook(std::string name){

and line 21

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std::string GradeBook::getCourseName(){

alternatively, you can add #using std::string after the header file inclusion.

Last edited by Ancient Dragon; Mar 18th, 2007 at 4:59 pm.

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Re: help with c++ classes

Mar 18th, 2007

thnx for the reply,
I have included that in the class' interface like this :

// implementation of class grade book's interface

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 c Syntax (Toggle Plain Text) 
#include <string>
using std::string;
//GradeBook's class definition
class GradeBook
{
public:
 GradeBook(string);
 void setCourseName(string);
 string getCourseName();
 void displayMessage();
private:
 string courseName;
}
#include <string>
using std::string;
//GradeBook's class definition
class GradeBook
{
public:
 GradeBook(string);
 void setCourseName(string);
 string getCourseName();
 void displayMessage();
private:
 string courseName;
}

I have tried what you said but i'm still in the rat race

Last edited by Ancient Dragon; Mar 19th, 2007 at 12:05 am. Reason: add code tags

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Re: help with c++ classes

Mar 19th, 2007

The problem is that the class must end with a semicolon. Put a semicolon after the closing brace on line 13 of the header file

Last edited by Ancient Dragon; Mar 19th, 2007 at 12:06 am.

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Re: help with c++ classes

Mar 19th, 2007

thnx but this is what i get:

--------------------Configuration: GradeBook - Win32 Debug--------------------
Compiling...
GradeBook.cpp
Linking...
LIBCD.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
Debug/GradeBook.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.
GradeBook.exe - 2 error(s), 0 warning(s)

pls can you do me a favor?
create the class interface yourself with the idea i have given and see if it works you can omit all the validations in member function setCourseName(), i hope i am not a pain in the ****....
if i am, i am sorry
i just can't proceed until i get this,

Last edited by addicted; Mar 19th, 2007 at 12:55 am.

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Re: help with c++ classes

Mar 19th, 2007

>LIBCD.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
You haven't defined your main() function. The linker doesn't know where the entry point of the application is.

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Re: help with c++ classes

Mar 19th, 2007

thanx alot,
please could you help me with my program, i have wrote about it in the early pages, go through it...... The error came when i put a semicolon at the end of my class interface, when i try to compile the class' source code, i get that message but when i remove the semicolon it brings back the previous error

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Re: help with c++ classes

#10

Mar 19th, 2007

This version compiles without errors. In this version I combined the .h and *.cpp into one *.cpp file for simplicity, but you should keep them separate if you wish. I also added the main() function at the bottom of the code. Hope this helps.

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
#include <iostream>
#include <string>
using std::cout;
using std::endl;
using std::string;
//GradeBook's class definition
class GradeBook
{
public:
GradeBook(string);
void setCourseName(string);
string getCourseName();
void displayMessage();
private:
string courseName;
};
 
//#include "GradeBook.h"// to tell the compiler i am using resources from class GradeBook
GradeBook::GradeBook(string name){
  setCourseName(name);
}
void GradeBook::setCourseName(string name){
 if(name.length() == 0){
  cout<<"\nName was not Entered";
 }
 if((name.length() > 0)&&(name.length() <=25)){
  courseName = name;
 }else 
  if(name.length()>25){
   courseName=name.substr(0,25);
   cout<<"\nName \""<<name<<"\" is more than 25 characters and has been truncated to 25"<<endl;
  }
}
string GradeBook::getCourseName(){
 return courseName;
}
void GradeBook::displayMessage(){
 
 cout<<"\nWelcome to the grade book of : "<<getCourseName()<<endl;
}
 
int main()
{
 
	return 0;
}
#include <iostream>
#include <string>
using std::cout;
using std::endl;
using std::string;
//GradeBook's class definition
class GradeBook
{
public:
GradeBook(string);
void setCourseName(string);
string getCourseName();
void displayMessage();
private:
string courseName;
};

//#include "GradeBook.h"// to tell the compiler i am using resources from class GradeBook
GradeBook::GradeBook(string name){
  setCourseName(name);
}
void GradeBook::setCourseName(string name){
 if(name.length() == 0){
  cout<<"\nName was not Entered";
 }
 if((name.length() > 0)&&(name.length() <=25)){
  courseName = name;
 }else 
  if(name.length()>25){
   courseName=name.substr(0,25);
   cout<<"\nName \""<<name<<"\" is more than 25 characters and has been truncated to 25"<<endl;
  }
}
string GradeBook::getCourseName(){
 return courseName;
}
void GradeBook::displayMessage(){
  
 cout<<"\nWelcome to the grade book of : "<<getCourseName()<<endl;
}

int main()
{

	return 0;
}