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Lynncake
 2 years ago
how do you search for a lastname in a linked list? c++
Lynncake
 2 years ago
how do you search for a lastname in a linked list? c++

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

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0I am using visual studio c++

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Did you implement the linked list yourself?

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0i did. ammm can you give me an example of a referenced variable?

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Referenced variable is like a pointer that is pretending to be deferenced.

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Okay I need to know what your code is like first of all.

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0bool 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; } }

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0It 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?

wio
 2 years ago
Best ResponseYou've already chosen the best response.1What is pnum supposed to be?

wio
 2 years ago
Best ResponseYou've already chosen the best response.1All you need to do is assign pnum to the pnum of the node with the correct name.

wio
 2 years ago
Best 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.

wio
 2 years ago
Best ResponseYou've already chosen the best response.1So 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 ```

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0I 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"; } }

wio
 2 years ago
Best 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; ```

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

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Okay, what sort of output are you getting? What is happening?

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0It 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"; }

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Alright, are you searching for something that is in the list?

wio
 2 years ago
Best 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.

wio
 2 years ago
Best 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.

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

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

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0yeah 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; }

wio
 2 years ago
Best ResponseYou've already chosen the best response.1why are you setting `p>phone` to `head>phone`?

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0those 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); };

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Yeah, 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.

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

wio
 2 years ago
Best ResponseYou've already chosen the best response.1If 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; ```

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Does that loop make sense so far? @Lynncake

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

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0PhoneBookItem* 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; }

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

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

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0yes it worked! thank you

wio
 2 years ago
Best 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`.

wio
 2 years ago
Best ResponseYou've already chosen the best response.1@Lynncake Does that make sense?

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0yes, it does thanks a lot

wio
 2 years ago
Best ResponseYou've already chosen the best response.1alright, well good luck then.

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0for 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.

wio
 2 years ago
Best ResponseYou've already chosen the best response.1The problem with this is that you need to keep track of the item before you.

wio
 2 years ago
Best ResponseYou've already chosen the best response.1And you set the guy behind you's `next` property to your own `next` property.

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0so in here i should hava another pointer that points to the next element?

wio
 2 years ago
Best ResponseYou've already chosen the best response.1This 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

wio
 2 years ago
Best ResponseYou've already chosen the best response.1For 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

wio
 2 years ago
Best 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 ```

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

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

wio
 2 years ago
Best ResponseYou've already chosen the best response.1For 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; } ```

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Hmmm, there should be a `return true;` in the check head part too.

wio
 2 years ago
Best ResponseYou've already chosen the best response.1What we are doing is changing this: dw:1364256150764:dw

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0so the last is the head?

wio
 2 years ago
Best ResponseYou've already chosen the best response.1To this: dw:1364256188626:dw

wio
 2 years ago
Best 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`

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0so i should create another pointer pointing to last?

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

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0i will, and thank you so much

Lynncake
 2 years ago
Best ResponseYou've already chosen the best response.0yes 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; }

wio
 2 years ago
Best ResponseYou've already chosen the best response.1There is nothing wrong with printing. The linked list is getting ruined by your delete somehow.

wio
 2 years ago
Best 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`

wio
 2 years ago
Best ResponseYou've already chosen the best response.1Your count idea id pretty interesting, though not as efficient it gets the job done.

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