C++ - Search an element in the Linked List

Searching an element in a linked list requires creating a temp node pointing to the head of the linked list. Along with this, two more variables are required to track search and track index of the current node. If the temp node is not null at the start, then traverse the linked list to check if current node value matches with the search value. If it matches then update search tracker variable and stop traversing the list, else keep on traversing the list. If the temp node is empty at the start, then the list contains no item.

The function SearchElement is created for this purpose. It is a 4-step process.

void SearchElement(int searchValue) {
  
  //1. create a temp node pointing to head
  Node* temp = head;
  
  //2. create two variables: found - to track
  //   search, idx - to track current index
  int found = 0;
  int i = 0;

  //3. if the temp node is not null check the
  //   node value with searchValue, if found 
  //   update variables and break the loop, else
  //   continue searching till temp node is not null 
  if(temp != NULL) {
    while(temp != NULL) {
      i++;
      if(temp->data == searchValue) {
        found++;
        break;
      }
      temp = temp->next;
    }
    if (found == 1) {
      cout<<searchValue<<" is found at index = "<<i<<".\n";
    } else {
      cout<<searchValue<<" is not found in the list.\n";
    }
  } else {
    
    //4. If the temp node is null at the start, 
    //   the list is empty
    cout<<"The list is empty.\n";
  }
}

The below is a complete program that uses above discussed concept to search an element in a given linked list.

#include <iostream>
using namespace std;

//node structure
struct Node {
    int data;
    Node* next;
};

class LinkedList {
  private:
    Node* head;
  public:
    LinkedList(){
      head = NULL;
    }

    //Add new element at the end of the list
    void push_back(int newElement) {
      Node* newNode = new Node();
      newNode->data = newElement;
      newNode->next = NULL; 
      if(head == NULL) {
        head = newNode;
      } else {
        Node* temp = head;
        while(temp->next != NULL)
          temp = temp->next;
        temp->next = newNode;
      }    
    }

    //Search an element in the list
    void SearchElement(int searchValue) {   
      Node* temp = head;
      int found = 0;
      int i = 0;

      if(temp != NULL) {
        while(temp != NULL) {
          i++;
          if(temp->data == searchValue) {
            found++;
            break;
          }
          temp = temp->next;
        }
        if (found == 1) {
          cout<<searchValue<<" is found at index = "<<i<<".\n";
        } else {
          cout<<searchValue<<" is not found in the list.\n";
        }
      } else {
        cout<<"The list is empty.\n";
      }
    } 

    //display the content of the list
    void PrintList() {
      Node* temp = head;
      if(temp != NULL) {
        cout<<"The list contains: ";
        while(temp != NULL) {
          cout<<temp->data<<" ";
          temp = temp->next;
        }
        cout<<endl;
      } else {
        cout<<"The list is empty.\n";
      }
    }    
};

// test the code 
int main() {
  LinkedList MyList;

  //Add three elements at the end of the list.
  MyList.push_back(10);
  MyList.push_back(20);
  MyList.push_back(30);

  //traverse to display the content of the list.
  MyList.PrintList();

  //search for element in the list
  MyList.SearchElement(10);
  MyList.SearchElement(15);
  MyList.SearchElement(20);

  return 0; 
}

The above code will give the following output:

The list contains: 10 20 30 
10 is found at index = 1.
15 is not found in the list.
20 is found at index = 2.