Its working in C, try this out. All test case passed SinglyLinkedListNode* insertNodeAtHead(SinglyLinkedListNode* llist, int data) {

SinglyLinkedListNode* temp = (SinglyLinkedListNode*)malloc(sizeof(SinglyLinkedListNode));
temp->data = data;
temp->next = NULL;

if(llist == NULL){
    llist = temp;
}else{
    temp->next = llist;
    llist = temp;
}
return llist;

}