Program to add numbers of any lenghth using linked lists

INFINITY ADDER

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SIZE 10001
struct node
{
	unsigned short int val;
	node* next;
}; 

struct result
{
	node* sum;
	int carry;
};

void make_list(char[],char[],node*&,node*&);
void free_list(result*&);
void free_list(node*&);
result* add_list(node*&,node*&);
void insert(node*&,int);

int main()
{
	FILE *fp;
	char n1[SIZE],n2[SIZE];
	node *node1=NULL,*node2=NULL,*temp=NULL;
	fp=fopen("input","r");
	fscanf(fp,"%s %s",n1,n2);
	make_list(n1,n2,node1,node2); 
	result* answer=add_list(node1,node2);
	if(answer!=NULL)
	{
		if(answer->carry)
			insert(answer->sum,answer->carry);
		for(temp=answer->sum;temp!=NULL;temp=temp->next)
				printf("%d",temp->val);
		printf("\n");
	}
	temp=NULL;
	free_list(node1);
	free_list(node2);
	free_list(answer);
	return 0;
}

void make_list(char a[],char b[],node *&node_a,node *&node_b)
{
	int l1=strlen(a);
	int l2=strlen(b);
	int i;
	for(i=l1-1;i>=0;i--)
		insert(node_a,(int)a[i]-(int)'0');
	for(i=l2-1;i>=0;i--)
		insert(node_b,(int)b[i]-(int)'0');
	if(l1>l2)
		for(i=0;i<l1-l2;i++)
			insert(node_b,0);
	else
		for(i=0;i<l2-l1;i++)
			insert(node_a,0);
}

void insert(node*&node1,int key)
{
	node *newnode=(node*)malloc(sizeof(struct node));
	newnode->val=key;
	newnode->next=NULL;
	if(node1!=NULL)
		newnode->next=node1;
	node1=newnode;
}

result* add_list(node*& node1,node*& node2)
{
	int sum=0;
	if(node1==NULL&&node2==NULL)
	{
		result *ans=(result*)malloc(sizeof(result));
		ans->sum=NULL;
		ans->carry=0;
		return ans;
	}
	result *ans=add_list(node1->next,node2->next);
	if(node1!=NULL)
		sum+=node1->val;
	if(node2!=NULL)
		sum+=node2->val;
	sum+=ans->carry;
	insert(ans->sum,sum%10);
	ans->carry=sum/10;
	return ans;
}
void free_list(result*& n)
{
	if(n!=NULL)
	{
		node* temp=n->sum;
		if(temp!=NULL)
		{
			node* save=temp->next;
			free(temp);
			temp=save;
		}
		free(n);
	}
	n=NULL;
}

void free_list(node*& temp)
{
	if(temp!=NULL)
	{
		node* save=temp->next;
		free(temp);
		temp=save;
	}
	temp=NULL;
}