error : Function definition is not allowed here

Question

It is showing errors in line 22 and 25

#include<bits/stdc++.h>

using namespace std;

class node{

public:

    int data;
    node *next;
    node (int data){
    this->data = data;
}

};

int main() {

     node *n1 = new node(10);
     node *n2 = new node(15);
     node *n3 = new node(20);

     node *head = n1;
     head->next = n2;
     n2->next = n3;
     n3->next = NULL;

     void main(){
         traverse(head);
     }
     void traverse(node head){
         node cur = head;

     }
 }

You can't define functions inside other functions. Now that someone formatted your code for you can you see the problem with the extra `main` function and the `traverse` function? — Retired Ninja, Nov 08 '21 at 08:32
why did you write `void main() { traverse(head); }` within `main` ? That makes no sense — 463035818_is_not_an_ai, Nov 08 '21 at 08:33
Please do not use `#include`: https://stackoverflow.com/questions/31816095/why-should-i-not-include-bits-stdc-h — MadScientist, Nov 08 '21 at 08:48

justANewb stands with Ukraine · Answer 1 · 2021-11-08T09:06:14.827

In main():

int main() {

     node *n1 = new node(10);
     node *n2 = new node(15);
     node *n3 = new node(20);

     node *head = n1;
     head->next = n2;
     n2->next = n3;
     n3->next = NULL;

     void main(){
         traverse(head);
     }
     void traverse(node head){
         node cur = head;

     }
 }

There are some problems:

In C++, you can't define a function inside a function.
Even if you don't define inside main(), you can't define two main() functions. Also, void main() isn't valid C++.

If you want to call traverse() when running the program, try:

class node
{
public:

    int data;
    node *next;
    node(int inputData = 0, node *inputNext = nullptr) : data{inputData}, next{inputNext} // ctor
    {

    }

    node (int data)
    {
         this->data = data;
    }

};

void traverse(node head)
{
    node cur = head;
}

int main()
{
    node *n1 = new node(10);
    node *n2 = new node(15);
    node *n3 = new node(20);

    node *head = n1;
    head->next = n2;
    n2->next = n3;
    n3->next = NULL;

    traverse(head);

}

Also, #include <bits/stdc++.h> and using namespace std; are all bad practice, so avoid using it.

`head` is a pointer but `traverse` expects a `node`. The code inside `traverse` won't work either if you fix the argument type. Admittedly not what they asked about, but that'll be the next error they'll get. Probably worth initializing `next` to nullptr in the constructor too. — Retired Ninja, Nov 08 '21 at 08:58

error : Function definition is not allowed here

1 Answers1