why exit code 139 at row no 47,what wrong in my code;

Question

#include <stdio.h>
#include <stdlib.h>

  struct node
  {
      int data;
      struct node*link;
  }*head;
  //fun to create linkedlist
   void createlist(int n);
   void traverslist();
   
int main()
{
    int n; //no of ele to be in linkedlist
    printf("enter total no of node:" );
    scanf("%d",&n);
    
    createlist(n);
    traverslist();
    
    return 0;
}

 void createlist(int n)
 {
    struct node *temp,*newnode;
    int data, i;
    head =(struct node *)malloc(sizeof(struct node));/*allocated first node*/
    //terminate if memory not allocated
    if (head=NULL)
    {
        printf("unable to allocate memory");
        exit(1);
    }
    
    // take input from user
    printf("enter the data of node 1:");
    scanf("%d",&data);
     
     head->data=data;
     head->link=NULL;
     
     temp=head;
     for(i=2;i<=n;i++)
     {
         newnode=malloc(sizeof(struct node));
         
         if (newnode=NULL)
         {
             printf("unable to allocate memory");
            break;
         }
         
         printf("enterthe data of node %d:",i);
         scanf("%d",&data);
         
         
        newnode->data=data;
        newnode->link=NULL;
        
        temp->link=newnode;
        temp=temp->link;
        
     }
    
 }
 
  void traverslist()
  {
      struct node *temp;
      if(head =NULL)
      { printf("list is empty");
      return ;}
      
      temp=head;
      int i=1;
      while(temp!=NULL)
      {printf(" data %d:%d\n",i,temp->data);
      temp= temp->link;
        i++;  
      }
  }

Answer 1

    head =(struct node *)malloc(sizeof(struct node));/*allocated first node*/
    printf("Before if comparison address of head %x\n",head);
    //terminate if memory not allocated
    if (head=NULL)
    {
        printf("unable to allocate memory");
        exit(1);
    }
    printf("After if comparison address of head %x\n",head);
    // take input from user
    

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What do you think does the red highlighted code do ??

Try to print the address of head before the If statement & after checking it.

Hint : Please check syntax to how to compare & the syntax to assign variables.

:)