Programming Forums > Application Development > C++

jasonfrost · Oct 26th, 2007, 10:42 PM

I am working on this program and as you'll see from the output, it prints out two objects. Now I am trying to include a 3rd object but I seem to be doing something wrong.

Here is the code...

(Toggle Plain Text)

#include <iostream>
using namespace std;

struct daytemps {               //struct to hold daily hi and low temperatures
        int day,hi,low,test;    //data members
        daytemps *next, *now;   //pointer to an object of struct type temp
};

void main() {
        daytemps *first, *tp;   //pointers to an object of struct type daytemps

        tp = new daytemps();    //create an unnamed object and assign the address to
                                //the pointer tp
        tp -> day = 1;          //put data in unnamed object
        tp -> hi = 98;
        tp -> low = 73;

        first = tp;             //assign the address of the unnamed object to the
                                //pointer first

        tp = new daytemps();    //create an unnamed object and assign the address to
                                //the pointer tp
        tp -> day = 2;          //put data in unnamed object
        tp -> hi = 95;
        tp -> low = 78;

        tp -> next = first;     //link the unnamed object to the object pointed to by
                                //first
        first = tp;             //assign the address of the unnamed object pointed
                                //to by tp to the pointer first; first should always
                                //point to the head of the list

        tp = new daytemps();

        tp -> day = 3;
        tp -> hi = 101;
        tp -> low = 70;

        tp -> next -> now = first;

        first = tp;

//*********output the data stored in the first element in the list*********
cout << first -> day << "---" << first -> hi << "---" << first -> low << endl;

//*********output the data stored in the second element in the list*********
cout << first -> next -> day << "---" << first -> next -> hi << "---"
     << first -> next -> low << endl;

cout << first -> next -> now -> day << "---" << first -> next -> now -> hi << "---" << first -> next -> now -> low << endl;

delete first -> next -> now;

delete first -> next;           //return the memory for the last object in the list to
                                //the free store of memory for reuse
delete first;                   //return the memory for the first object in the list to
                                //the free store of memory ro reuse
}

#include <iostream>
using namespace std;

struct daytemps {               //struct to hold daily hi and low temperatures
        int day,hi,low,test;    //data members
        daytemps *next, *now;   //pointer to an object of struct type temp
};

void main() {
        daytemps *first, *tp;   //pointers to an object of struct type daytemps

        tp = new daytemps();    //create an unnamed object and assign the address to
                                //the pointer tp
        tp -> day = 1;          //put data in unnamed object
        tp -> hi = 98;
        tp -> low = 73;

        first = tp;             //assign the address of the unnamed object to the
                                //pointer first

        tp = new daytemps();    //create an unnamed object and assign the address to
                                //the pointer tp
        tp -> day = 2;          //put data in unnamed object
        tp -> hi = 95;
        tp -> low = 78;

        tp -> next = first;     //link the unnamed object to the object pointed to by
                                //first
        first = tp;             //assign the address of the unnamed object pointed
                                //to by tp to the pointer first; first should always
                                //point to the head of the list

        tp = new daytemps();

        tp -> day = 3;
        tp -> hi = 101;
        tp -> low = 70;

        tp -> next -> now = first;

        first = tp;

//*********output the data stored in the first element in the list*********
cout << first -> day << "---" << first -> hi << "---" << first -> low << endl;

//*********output the data stored in the second element in the list*********
cout << first -> next -> day << "---" << first -> next -> hi << "---"
     << first -> next -> low << endl;

cout << first -> next -> now -> day << "---" << first -> next -> now -> hi << "---" << first -> next -> now -> low << endl;

delete first -> next -> now;

delete first -> next;           //return the memory for the last object in the list to
                                //the free store of memory for reuse
delete first;                   //return the memory for the first object in the list to
                                //the free store of memory ro reuse
}

It compiles fine but when I run it I get a "core dump".

Any pointers you could give would be great. Thanks.

DaWei · Oct 26th, 2007, 10:52 PM

I'm going to tell you what I tell nearly every one that comes here with a linked list problem. Get a pencil and paper. Go through your code, line by line, and construct the nodes and pointers just as you have instructed the processor to do. When you're through, "print it out" by following your instructions. Don't do it by memory or perception of what you think you've done. Do it precisely by your own written instructions.

If you don't find all your problems, post back.

lectricpharaoh · Oct 28th, 2007, 7:53 AM

Quote:

Originally Posted by DaWei

Get a pencil and paper. Go through your code, line by line

Amen. Of course, it's helpful for many more problems than just linked list ones.

mrynit · Oct 28th, 2007, 10:53 PM

Working it on paper is how i solved the process. It took me about seven pages. Draw a rectangle for each node. Divide the rectange into three parts and draw arrows connecting the appropriate parts together. go throught the process of making a new node and assigning values step by step on paper.

I have posted a working linked list example in java if you want to look it up.

By the way you used void main instead of int main. You need return 0 as well.

grumpy · Oct 29th, 2007, 2:17 AM

I'll take pity.

(Toggle Plain Text)

        tp = new daytemps();

        tp -> day = 3;
        tp -> hi = 101;
        tp -> low = 70;

        tp -> next -> now = first;

is one cause of problem. tp->next is uninitialised. So assigning tp->next->now yields undefined behaviour.

Oct 26th, 2007, 10:42 PM	#1
jasonfrost Newbie Join Date: Aug 2007 Posts: 21 Rep Power: 0	Linked lists problem I am working on this program and as you'll see from the output, it prints out two objects. Now I am trying to include a 3rd object but I seem to be doing something wrong. Here is the code... (Toggle Plain Text) #include <iostream> using namespace std; struct daytemps { //struct to hold daily hi and low temperatures int day,hi,low,test; //data members daytemps next, now; //pointer to an object of struct type temp }; void main() { daytemps first, tp; //pointers to an object of struct type daytemps tp = new daytemps(); //create an unnamed object and assign the address to //the pointer tp tp -> day = 1; //put data in unnamed object tp -> hi = 98; tp -> low = 73; first = tp; //assign the address of the unnamed object to the //pointer first tp = new daytemps(); //create an unnamed object and assign the address to //the pointer tp tp -> day = 2; //put data in unnamed object tp -> hi = 95; tp -> low = 78; tp -> next = first; //link the unnamed object to the object pointed to by //first first = tp; //assign the address of the unnamed object pointed //to by tp to the pointer first; first should always //point to the head of the list tp = new daytemps(); tp -> day = 3; tp -> hi = 101; tp -> low = 70; tp -> next -> now = first; first = tp; //*******output the data stored in the first element in the list***** cout << first -> day << "---" << first -> hi << "---" << first -> low << endl; //*****output the data stored in the second element in the list******* cout << first -> next -> day << "---" << first -> next -> hi << "---" << first -> next -> low << endl; cout << first -> next -> now -> day << "---" << first -> next -> now -> hi << "---" << first -> next -> now -> low << endl; delete first -> next -> now; delete first -> next; //return the memory for the last object in the list to //the free store of memory for reuse delete first; //return the memory for the first object in the list to //the free store of memory ro reuse } #include <iostream> using namespace std; struct daytemps { //struct to hold daily hi and low temperatures int day,hi,low,test; //data members daytemps next, now; //pointer to an object of struct type temp }; void main() { daytemps first, tp; //pointers to an object of struct type daytemps tp = new daytemps(); //create an unnamed object and assign the address to //the pointer tp tp -> day = 1; //put data in unnamed object tp -> hi = 98; tp -> low = 73; first = tp; //assign the address of the unnamed object to the //pointer first tp = new daytemps(); //create an unnamed object and assign the address to //the pointer tp tp -> day = 2; //put data in unnamed object tp -> hi = 95; tp -> low = 78; tp -> next = first; //link the unnamed object to the object pointed to by //first first = tp; //assign the address of the unnamed object pointed //to by tp to the pointer first; first should always //point to the head of the list tp = new daytemps(); tp -> day = 3; tp -> hi = 101; tp -> low = 70; tp -> next -> now = first; first = tp; //*******output the data stored in the first element in the list***** cout << first -> day << "---" << first -> hi << "---" << first -> low << endl; //*****output the data stored in the second element in the list******* cout << first -> next -> day << "---" << first -> next -> hi << "---" << first -> next -> low << endl; cout << first -> next -> now -> day << "---" << first -> next -> now -> hi << "---" << first -> next -> now -> low << endl; delete first -> next -> now; delete first -> next; //return the memory for the last object in the list to //the free store of memory for reuse delete first; //return the memory for the first object in the list to //the free store of memory ro reuse } It compiles fine but when I run it I get a "core dump". Any pointers you could give would be great. Thanks.

Oct 26th, 2007, 10:52 PM	#2
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Re: Linked lists problem I'm going to tell you what I tell nearly every one that comes here with a linked list problem. Get a pencil and paper. Go through your code, line by line, and construct the nodes and pointers just as you have instructed the processor to do. When you're through, "print it out" by following your instructions. Don't do it by memory or perception of what you think you've done. Do it precisely by your own written instructions. If you don't find all your problems, post back. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Oct 28th, 2007, 10:53 PM	#4
mrynit Hobbyist Programmer Join Date: Mar 2006 Location: WA, USA Posts: 332 Rep Power: 3	Re: Linked lists problem Working it on paper is how i solved the process. It took me about seven pages. Draw a rectangle for each node. Divide the rectange into three parts and draw arrows connecting the appropriate parts together. go throught the process of making a new node and assigning values step by step on paper. I have posted a working linked list example in java if you want to look it up. By the way you used void main instead of int main. You need return 0 as well. __________________ i dont know much about programming but i try to help

Oct 29th, 2007, 2:17 AM	#5
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,223 Rep Power: 5	Re: Linked lists problem I'll take pity. (Toggle Plain Text) tp = new daytemps(); tp -> day = 3; tp -> hi = 101; tp -> low = 70; tp -> next -> now = first; tp = new daytemps(); tp -> day = 3; tp -> hi = 101; tp -> low = 70; tp -> next -> now = first; is one cause of problem. tp->next is uninitialised. So assigning tp->next->now yields undefined behaviour.

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Programming Forums > Application Development > C++

Linked lists problem