Insert at first and end

#include <stdio.h>
#include <stdlib.h>
typedef struct data{
    int age;
    struct data *next;
}data;

    data *head;

void insert_at_end(int a)
{
    data *temp;
    temp = (data*)malloc(sizeof(data));
    temp -> age = a;
    temp -> next = NULL;

    if(head == NULL){
        head = temp;
        return;
    }
    else
    data *node = head;
    while(node -> next != NULL)
    {
        node -> next = temp;
    }
    node-> next = temp;
}

void insert_at_first(int a)
{
    data *temp;
    temp = (data*)malloc(sizeof(data));
    temp -> age = a;
    temp -> next = NULL;

    temp -> next = head;
    head = temp;
}

void print()
{
    data *temp = head;

    while(temp != NULL){
        printf("%d ",temp ->age);
        temp = temp -> next;
        }
        printf("\n");
}

int main()
{
    head = NULL;
    int in;


    insert_at_end(5);
    insert_at_first(4);
    insert_at_first(3);
    insert_at_end(9);

    print();
}