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Yona · Jan 16th, 2006, 3:46 AM

hi,
i am working on this assignment. i have a header IntNode given and based on this header i have to make a new header InrNodeEx in which i have to make the three following functions :
-inline int list_sum(const IntNode *head)
Returns sumary of list
-inline void list_multilpy_withNumber(IntNode *head, int number)
Multiplies all elements of list with a number
-inline IntNode* list_from_multiplyWithNumber(const IntNode* source, int number)
Multiplies all elements of list with a number without changing the source list
IntNodeEx i've written is the following

(Toggle Plain Text)

#include "IntNode.h"

//Returns sumary of list 
inline int list_sum(const IntNode *head){ 
IntNode *current; 
int sum=0; 
current=head; //ERROR APPEARS HERE//
while(current){ 
sum = sum + current->data; 
current=current->getNext(); 
} 
return sum; 
} 


//Multiplies all elements of list with a number 
inline void list_multilpy_withNumber(IntNode *head, int number){ 
IntNode *current=head; 
while(current){ 
current->data=(current->data)*number; 
current=current->getNext(); 
} 
} 

//Multiplies all elements of list with a number without changing the source list 
inline IntNode* list_from_multiplyWithNumber(const IntNode* source, int number){ 
IntNode *current=source; //ERROR APPEARS HERE//
IntNode *target=0; 
while(current){ 
list_insert(&target, new IntNode((current->data)*number)); 
current=current->getNext(); 
} 
return target; 
}

the problem is that when i call the functions list_sum(const IntNode *) and list_from_multiplyWithNumber(const IntNode*, int) the compiler shows the following mistakes
In function `int list_sum(const IntNode*)':nvalid
conversion from `const IntNode*' to `IntNode*'
In function `IntNode* list_from_multiplyWithNumber(const IntNode*, int)':invalid conversion from `const IntNode*' to `IntNode*'
which is absolutely normal to happen but i really can't figure out any way to deal with these errors.

Can anybody suggest any solution?
thanx for ur time!!!!

grumpy · Jan 16th, 2006, 4:37 AM

The reason for the error is that the argument to both functions is a const pointer, but you're attempting to copy it to a non-const pointer. Doing such a thing would provide a direct means of modifying a const object, and the compiler refuses.

The solution is to use a technique that does not (implicitly or explicitly) to remove the const'ness of the pointer. A poor solution (which, if the person marking your exercise is awake, would result in lower marks) would be to bludgeon the compiler into submission by using a typecast.

Is getNext() a const method of IntNode? If it is, you will not need to use a typecast. If it isn't, then whoever gave you the assignment should be shot as the only solution would be to use a typecast.

Are you allowed to use recursion?

The Dark · Jan 16th, 2006, 6:53 PM

As grumpy said, you are copying the const pointer to a non-const variable. Try changing your local pointers to const.
In list_sum, change

(Toggle Plain Text)

IntNode *current;

to

(Toggle Plain Text)

const IntNode *current;

Yona · Feb 1st, 2006, 4:41 AM

hi again,
thanx for ur help so far. by the way when i asked the tutor recently he said that in function list_from_multiplyWithNumber i should use the function list_multiplyWithNumber, but i stil, l cant figure out how to use it...

nnxion · Feb 1st, 2006, 4:58 AM

Quote:

Originally Posted by Yona

when i asked the tutor recently he said that in function list_from_multiplyWithNumber i should use the function list_multiplyWithNumber

What did he say?

Jan 16th, 2006, 3:46 AM	#1
Yona Newbie Join Date: Jan 2006 Posts: 2 Rep Power: 0	*invalid conversion from `const IntNode' to `IntNode'* hi, i am working on this assignment. i have a header IntNode given and based on this header i have to make a new header InrNodeEx in which i have to make the three following functions : -inline int list_sum(const IntNode head) Returns sumary of list -inline void list_multilpy_withNumber(IntNode head, int number) Multiplies all elements of list with a number -inline IntNode* list_from_multiplyWithNumber(const IntNode* source, int number) Multiplies all elements of list with a number without changing the source list IntNodeEx i've written is the following (Toggle Plain Text) #include "IntNode.h" //Returns sumary of list inline int list_sum(const IntNode head){ IntNode current; int sum=0; current=head; //ERROR APPEARS HERE// while(current){ sum = sum + current->data; current=current->getNext(); } return sum; } //Multiplies all elements of list with a number inline void list_multilpy_withNumber(IntNode head, int number){ IntNode current=head; while(current){ current->data=(current->data)number; current=current->getNext(); } } //Multiplies all elements of list with a number without changing the source list inline IntNode list_from_multiplyWithNumber(const IntNode* source, int number){ IntNode current=source; //ERROR APPEARS HERE// IntNode target=0; while(current){ list_insert(&target, new IntNode((current->data)number)); current=current->getNext(); } return target; } #include "IntNode.h" //Returns sumary of list inline int list_sum(const IntNode head){ IntNode current; int sum=0; current=head; //ERROR APPEARS HERE// while(current){ sum = sum + current->data; current=current->getNext(); } return sum; } //Multiplies all elements of list with a number inline void list_multilpy_withNumber(IntNode head, int number){ IntNode current=head; while(current){ current->data=(current->data)number; current=current->getNext(); } } //Multiplies all elements of list with a number without changing the source list inline IntNode* list_from_multiplyWithNumber(const IntNode* source, int number){ IntNode current=source; //ERROR APPEARS HERE// IntNode target=0; while(current){ list_insert(&target, new IntNode((current->data)number)); current=current->getNext(); } return target; } the problem is that when i call the functions list_sum(const IntNode ) and list_from_multiplyWithNumber(const IntNode, int) the compiler shows the following mistakes In function `int list_sum(const IntNode)':nvalid conversion from `const IntNode' to `IntNode' In function `IntNode* list_from_multiplyWithNumber(const IntNode, int)':invalid conversion from `const IntNode' to `IntNode*' which is absolutely normal to happen but i really can't figure out any way to deal with these errors. Can anybody suggest any solution? thanx for ur time!!!!

Jan 16th, 2006, 6:53 PM	#3
The Dark Expert Programmer Join Date: Jun 2005 Posts: 852 Rep Power: 4	As grumpy said, you are copying the const pointer to a non-const variable. Try changing your local pointers to const. In list_sum, change (Toggle Plain Text) IntNode current; IntNode current; to (Toggle Plain Text) const IntNode current; const IntNode current;

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Jan 16th, 2006, 4:37 AM	#2
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,223 Rep Power: 5	The reason for the error is that the argument to both functions is a const pointer, but you're attempting to copy it to a non-const pointer. Doing such a thing would provide a direct means of modifying a const object, and the compiler refuses. The solution is to use a technique that does not (implicitly or explicitly) to remove the const'ness of the pointer. A poor solution (which, if the person marking your exercise is awake, would result in lower marks) would be to bludgeon the compiler into submission by using a typecast. Is getNext() a const method of IntNode? If it is, you will not need to use a typecast. If it isn't, then whoever gave you the assignment should be shot as the only solution would be to use a typecast. Are you allowed to use recursion?

Feb 1st, 2006, 4:41 AM	#4
Yona Newbie Join Date: Jan 2006 Posts: 2 Rep Power: 0	hi again, thanx for ur help so far. by the way when i asked the tutor recently he said that in function list_from_multiplyWithNumber i should use the function list_multiplyWithNumber, but i stil, l cant figure out how to use it...

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