Question

Hi I would like to see an example in c++
of Stack As Linked List 
I need a seek() function which receives a double number X 
and which returns in which position in the stack is X.
If the value X is not in the stack, the function should return -1

Answer 1

Code for the function seek() only:

int seek(double x){
    struct Node *ptr;
    if(top == NULL)
        return -1;//if stack is empty return -1
    ptr = top;
    int position = 1;//we consider the top position to be the first position
    while(ptr != NULL){
        if(ptr->data == x)
            return position;
        else{ 
            ptr = ptr->next;
            position++;//update position as we move forward in the list
        }
    }
    return -1;
}

Full working code:

#include <iostream>
using namespace std;
struct Node {//node definition
   double data;
   struct Node *next;
};
struct Node* top = NULL;
void push(double val) {//pushes the new node
   struct Node* newnode = (struct Node*) malloc(sizeof(struct Node));
   newnode->data = val;
   newnode->next = top;
   top = newnode;
}
void pop() {//pops the top element from the stack
   if(top==NULL)
   cout<<"Stack Underflow"<<endl;
   else {
      cout<<"The popped element is "<< top->data <<endl;
      top = top->next;
   }
}

int seek(double x){
    struct Node *ptr;
    if(top == NULL)
        return -1;//if stack is empty return -1
    ptr = top;
    int position = 1;//we consider the top position to be the first position
    while(ptr != NULL){
        if(ptr->data == x)
            return position;
        else{ 
            ptr = ptr->next;
            position++;//update position as we move forward in the list
        }
    }
    return -1;
}

void display() {
   struct Node* ptr;
   if(top==NULL)
   cout<<"stack is empty";
   else {
      ptr = top;
      cout<<"Stack elements are: ";
      while (ptr != NULL) {
         cout<< ptr->data <<" ";
         ptr = ptr->next;
      }
   }
   cout<<endl;
}
int main() {
   int ch;
   double val;
   cout<<"1) Push in stack"<<endl;
   cout<<"2) Pop from stack"<<endl;
   cout<<"3) Display stack"<<endl;
   cout<<"4) Seek function"<<endl;
   cout<<"5) Exit"<<endl;
   do {
      cout<<"Enter choice: "<<endl;
      cin>>ch;
      switch(ch) {
         case 1: {
            cout<<"Enter value to be pushed:"<<endl;
            cin>>val;
            push(val);
            break;
         }
         case 2: {
            pop();
            break;
         }
         case 3: {
            display();
            break;
         }
         case 4: {
             cout<<"Enter value : ";
             double x;
             cin>>x;
             int position = seek(x);
             cout<<"The postion is "<<position<<endl;
             break;
         }
         case 5: {
            cout<<"Exit"<<endl;
            break;
         }
         default: {
            cout<<"Invalid Choice"<<endl;
         }
      }
   }while(ch!=5);
   return 0;
}

output:

code screenshot: