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Lynncake
Group Title
how do you search for a lastname in a linked list? c++
 one year ago
 one year ago
Lynncake Group Title
how do you search for a lastname in a linked list? c++
 one year ago
 one year ago

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Lynncake Group TitleBest ResponseYou've already chosen the best response.0
i have a linked list that stores firstname, lastname, and phone number. i need to find the lastname
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
Are you using the STL?
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
I am using visual studio c++
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
Did you implement the linked list yourself?
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
i did. ammm can you give me an example of a referenced variable?
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
Referenced variable is like a pointer that is pretending to be deferenced.
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
Okay I need to know what your code is like first of all.
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
bool PhoneBook::Lookup (const string& lname, const string& fname, string& pnum) const { PhoneBookItem* p = head; PhoneBookItem* q = head>next; if (head == NULL) return false; else if (lname == p>lastname) { if (fname == p>firstname) { return true; } else return false; } else { while (q != NULL && lname != q>lastname) { p = q; } if (q != NULL && lname == q>lastname) if (fname == q>firstname) return true; else return false; else return false; } }
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
It says that the pnum should be returned to the calling function via a third argument, a reference variable. I don't know how. can you help me with this?
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
What is pnum supposed to be?
 one year ago

SnuggieLad Group TitleBest ResponseYou've already chosen the best response.0
wio..phone number
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
All you need to do is assign pnum to the pnum of the node with the correct name.
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
``` while (q != NULL && lname != q>lastname) { p = q; } ``` This code doesn't make sense. You should try something like: ``` while (q != NULL && lname != q>lastname) { p = q; q = q>next; } ``` You need to update q and p.
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
So assuming you find it, before you return true, you wanna assign pnum. ``` if (fname == p>firstname) { pnum = q>pnum; // put it here return true; } ``` ``` if (fname == q>firstname) { pnum = q>pnum; // here too return true; } else ```
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
I tried that, but it doesn't work. Here is the code in the main. void LookupEntry(const PhoneBook& pb) { string last, first, phone; cout << "Enter last name: "; cin >> last; cout << "Enter first name: "; cin >> first; bool success = pb.Lookup(last, first, phone); if (success) { cout << "\nThe phone number is " << phone << ". \n"; } else { cout << "\nError: no one by this name is in the phone book.\n"; } }
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
``` string last, first, phone; ``` The problem is that `phone` should be a reference. ``` string last, first; string& phone; ```
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
Does it even compile?
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
It does, but that code in the main cannot be changed since our professor said so.
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
Okay, what sort of output are you getting? What is happening?
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
It outputs : Error: no one by this name is in the phone book. ================================================= if (success) { cout << "\nThe phone number is " << phone << ". \n"; } else { cout << "\nError: no one by this name is in the phone book.\n"; }
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
Alright, are you searching for something that is in the list?
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
``` else if (lname == p>lastname) { if (fname == p>firstname) { return true; } else return false; } ``` This code is wrong. If the last name is correct but the first name is not correct, it should continue searching, but your code instead gives up entirely.
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
``` else if (lname == p>lastname && fname == p>firstname) { return true; } ``` This is what you should be doing.
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
There are a lot of bugs in your code, it'd be easier to show the correct way...
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
For example, why have `p` and `q`? You only need one to keep track of where you are, right?
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
yeah but i need to test this ============================================= if (head == NULL) return false; else if (lname == p>lastname && fname == p>firstname) { p>phone = head>phone; return true; } else { while (q != NULL && lname != q>lastname) { p = q; p = p>next; } if (q != NULL && lname == q>lastname && fname == q>firstname) { q>phone = head>phone; return true; } else return false; } ===================================== else { while (q != NULL && lname != q>lastname) { p = q; p = p>next; } if (q != NULL && lname == q>lastname && fname == q>firstname) { q>phone = head>phone; return true; } else return false; }
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
why are you setting `p>phone` to `head>phone`?
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
those are the variable in my struct ====================================================== struct PhoneBookItem { string lastname; string firstname; string phone; PhoneBookItem* next; PhoneBookItem(const string& l, const string& f, const string& ph); };
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
Yeah, but you're setting the current item `p` to have the same phone number as the first item `head`. There is no reason to do that.
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
Okay, you should start out with your current item point to the front: ``` PhoneBookItem* current = head; ```
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
yes i did that
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
If you go through the whole list without finding it, then you want to return false. ``` while (current != NULL) { // search code here current = current>next } return false; ```
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
Does that loop make sense so far? @Lynncake
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
yes it does, i'm writing the rest of it. but i am not sure if this is right
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
PhoneBookItem* p = head; if (head == NULL) return false; else { while (p != NULL) { if (lname == p>lastname && fname == p>firstname) { return true; } p = p>next; } return false; }
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
Now, for the search code... we just check if the names are correct ``` if (current>firstname == fname && current>lastname == lname) { pnum = current>phone; return true; } ```
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
We don't have anything if the names don't match. The loop will take care of that for us.
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
yes it worked! thank you
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
One second though.
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
``` if (head == NULL) return false; else { while (p != NULL) ``` The `if (head == NULL)` here is pointless. The `while (p != NULL)` already check if `head` is `NULL`.
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
@Lynncake Does that make sense?
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
yes, it does thanks a lot
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
alright, well good luck then.
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
for the delete, is this right? ====================================== PhoneBookItem* p = head; while (p != NULL) { if (lname == p>lastname && fname == p>firstname) { delete p; p>next=NULL; num; return true; } p = p>next; } return false; ====================================== I followed your method/concept.
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
The problem with this is that you need to keep track of the item before you.
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
And you set the guy behind you's `next` property to your own `next` property.
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
so in here i should hava another pointer that points to the next element?
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
This case is a bit tricky because you have two case: 1) They are deleting the head... 2) They are deleting something in the middle of the list
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
For 1) you delete it, and set head to NULL For 2) you need to set the previous guy's next to the deleted guy's next
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
``` PhoneBookItem* last = head; PhoneBookItem* current = head>next; // Check head // Check guys in the middle of the list ```
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
For check head, we wanna do: ``` if (head != NULL && head>firstname == fname && head>lastname == lname) { delete head; head = NULL; } ```
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
For checking others, we want a loop: ``` while (current != NULL) { \\ check current last = current; current = current>next; } return false; ```
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
For current, we do something similar to head, but with a change: ``` if (current>firstname == fname && current>lastname == lname) { last>next = current>next; delete head; return true; } ```
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
Hmmm, there should be a `return true;` in the check head part too.
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
What we are doing is changing this: dw:1364256150764:dw
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
so the last is the head?
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
To this: dw:1364256188626:dw
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
`last` starts out as the head in the beginning. But last is set to `current` every time go move to the next element. `last` is just storing what comes before `current`
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
so i should create another pointer pointing to last?
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
I gotta brb for a bit, but look at the code I posted if you are confused
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
i will, and thank you so much
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
yes it did delte, but now my printing is messed up after deleting ============================================== ///////////////////////DELETE//////////////////////////////////////// PhoneBookItem* p = head; PhoneBookItem* q; int count=0; while (p != NULL) { if (count==0) { if (p>firstname == fname && p>lastname == lname) { delete head; head = NULL; num; return true; } } else if (count>0) { if (p>firstname == fname && p>lastname == lname) { q>next = p>next; delete head; num; return true; } } q = p; p = p>next; count++; } return false; ============================================= ///////////////////////////////PRINT///////////////////////////////// ostream& operator << (ostream& out, const PhoneBook& pbook) { PhoneBookItem* p = pbook.head; while (p != NULL) { out <<p>lastname<<", "<<p>firstname<<": "<<p>phone<<endl; p = p>next; } return out; }
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
There is nothing wrong with printing. The linked list is getting ruined by your delete somehow.
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
``` if (p>firstname == fname && p>lastname == lname) { q>next = p>next; delete head; num; return true; } ``` You should be deleting `p` here not `head`
 one year ago

wio Group TitleBest ResponseYou've already chosen the best response.1
Your count idea id pretty interesting, though not as efficient it gets the job done.
 one year ago

Lynncake Group TitleBest ResponseYou've already chosen the best response.0
thank you so much. now i can study my other classes. ^_^ THANK YOU!!!!
 one year ago
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