I am trying to implement a tree with infinite nodes but its giving SEGMENTATION FAULT as an error?

Question

I was making a project where you can search for a ques where I was implementing tree as in the ques asked would be divided into words and questions would be stored in words in form of tree for example

        root
      /   |  \
   what where why
  /  |    | \   \  \
 is are  is are  is are 

but its giving me error while trying to access the array inside the structure.

#include <bits/stdc++.h>
using namespace std;

struct node{
    string  ques;
    string ans;
    node* child[100];
    int noc;
    node(string word){
        noc=0;
        ques=word;
        child[0] = NULL;
    }
};

node* findnode(node* pnode,string q){
    for(int i=0;i<pnode->noc;i++){
        if(pnode->child[i]->ques==q){
            return pnode->child[i];
        }
    }
    return NULL;
}

node* createnode(node* pnode,string word){
    node* childnode= new node(word);
    pnode->child[pnode->noc++]=childnode;
    return childnode;
}

string ansnode(node* pnode){
    return pnode->ans;
}

void storeans(node* pnode,string ans2){
    pnode->ans=ans2;
}

int main(){
    node* root=new node("root");
    node* p= root;
    string s[4]={"What","is","your","name"};
    
    for(int i=0;i<4;i++){
        p = findnode(p,s[i]);
        if(!p){
            p=createnode(p,s[i]);
        }
    }
    
    
    return 0;
}

I am kind off new to this and was doing this for my project, so pardon if I am doing something silly.

Error is [Done] exited with code=3221225477 in 1.484 seconds

Answer 1

The logic is wrong here:

    p = findnode(p,s[i]);
    if(!p){
        p=createnode(p,s[i]);
    }

findnode returns NULL when it cannot find a child in p with s[i]. You check if it is NULL via if (!p) and then you are calling createnode(p,s[i]) to add a child at p, but p is NULL. Eventually pnode->child[pnode->noc++]=childnode; is undefined behavior because you are dereferencing a nullptr.

If you cannot find the node then you want to add a child at the current node, not at the NULL that findnode returned to indicate that it could not find the child:

    auto next = findnode(p,s[i]);
    if(!next){
        next=createnode(p,s[i]);
    }
    p = next;

If you had used a debugger you could have seen that p passed to createnode was a nullptr.