I am making a LinkedList class in C with its methods, like adding nodes, traversing, and searching. When implementing the search function, it seems not working properly because it does not find the value in linked list when in fact it is inside the linked list. The code is shown below.

#include <iostream>

class Node {
    public:
        int value;
        Node* next;
        
        Node(int value, Node* next) {
            this->value = value;
            this->next = next;
        }
};

class LinkedList {
public:
    Node* head;
    Node* tail;
    
    LinkedList() {
        this->head = nullptr;
        this->tail = nullptr;
    }
    
    LinkedList(Node* node) {
        this->head = node;
        this->tail = node;
    }
    
    void addNodeFront(Node* node) {
        if(head==nullptr && tail==nullptr) {
            this->head = node;
            this->tail = node;
            return;
        }
        this->tail = this->head;
        this->head = node;
        node->next = tail;
    }
    
    void addNodeBack(Node* node) {
        if(head==nullptr && tail==nullptr) {
            this->head = node;
            this->tail = node;
            return;
        }
        this->tail->next = node;
        this->tail = node;
    }
    
    void addNodeAfterNode(Node* prevNode, Node* node) {
        node->next = prevNode->next;
        prevNode->next = node;
    }
    
    bool searchVal(int val) {
        while(this->head != nullptr) {
            if(this->head->value == val) return true;
            this->head = this->head->next;
        }
        return false;
    }
    
    void deleteNode(Node* node) {
        Node* prevNode = this->head;
        while(prevNode->next != node) {
            
        }
    }
    
    void traverseLinkedList() {
        while(this->head!=nullptr) {
            std::cout << this->head->value << "->";
            this->head = this->head->next;
        }
        std::cout << "\n";
    }

    void sortLinkedList() {
        
    }
};

int main() {
    Node node1(2,nullptr);
    Node node2(4,nullptr);
    Node node3(3,nullptr);
    LinkedList ls;
    ls.addNodeFront(&node1);
    ls.addNodeBack(&node3);
    ls.addNodeAfterNode(&node3, &node2);
    ls.traverseLinkedList();
    if(ls.searchVal(4)) std::cout << "value found\n";
    else std::cout << "value not found\n";
}

When I call the searchVal() function inside the main function it outputs value not found while value 4 is inside the linked list. What is wrong with my code?

CodePudding user response：

When I call the searchVal() function inside the main function it outputs value not found while value 4 is inside the linked list. What is wrong with my code?

Just before you call searchVal(4) you call traverseLinkedList(), and traverseLinkedList() is implemented in such a way that when it returns, this->head will be NULL, which means that at that point your linked list is empty (and you have leaked memory). You'll want to modify traverseLinkedList() and searchVal() to not change the value of this->head (or any other member-variables of the LinkedList object) so that they don't modify the state of the list as a side effect.