WAP to combine two sorted link list using merge sort

#include<stdio.h>
#include<conio.h>
struct node
{
int n;
struct node *next;
}*first=NULL,*first2=NULL,*first3=NULL,*temp,*temp1,*temp2,*temp3;
void insert(int x)
{
temp=(struct node*)malloc(sizeof(struct node));
temp->n=x;
if(first==NULL)
{
temp->next=NULL;
first=temp;
}
else
{
temp1=first;
while(temp1->next->n<x && temp1->next!=NULL)
{
temp1=temp1->next;
}
if(temp1==first && temp1->n>x)
{
temp->next=first;
first=temp;
}
else
{
temp->next=temp1->next;
temp1->next=temp;
}
}
}
void insert2(int x)
{
temp=(struct node*)malloc(sizeof(struct node));
temp->n=x;
if(first2==NULL)
{
temp->next=NULL;
first2=temp;
}
else
{
temp1=first2;
while(temp1->next->n<x && temp1->next!=NULL)
{
temp1=temp1->next;
}
if(temp1==first2 && temp1->n>x)
{
temp->next=first2;
first2=temp;
}
else
{
temp->next=temp1->next;
temp1->next=temp;
}
}
}
void display()
{
if(first==NULL)
{
printf("Stack is empty");
return;
}
temp=first;
while(temp!=NULL)
{
printf("\n%d",temp->n);
temp=temp->next;
}
}
void display2()
{
if(first2==NULL)
{
printf("Stack is empty");
return;
}
temp=first2;
while(temp!=NULL)
{
printf("\n%d",temp->n);
temp=temp->next;
}
}
void display3()
{
if(first3==NULL)
{
printf("Stack is empty");
return;
}
temp=first3;
while(temp!=NULL)
{
printf("\n%d",temp->n);
temp=temp->next;
}
}
void merge()
{
temp2=first;
temp3=first2;
while(temp2!=NULL && temp3!=NULL)
{
temp=(struct node*)malloc(sizeof(struct node));
if(temp2->n<temp3->n)
{
temp->n=temp2->n;
temp2=temp2->next;
}
else
{
temp->n=temp3->n;
temp3=temp3->next;
}
if(first3==NULL)
{
first3=temp;
}
else
{
temp1->next=temp;
}
temp1=temp;
temp->next=NULL;
}
while(temp2!=NULL)
{
temp=(struct node*)malloc(sizeof(struct node));
temp->n=temp2->n;
temp2=temp2->next;
temp1->next=temp;
temp1=temp;
temp->next=NULL;
}
while(temp3!=NULL)
{
temp=(struct node*)malloc(sizeof(struct node));
temp->n=temp3->n;
temp3=temp3->next;
temp1->next=temp;
temp1=temp;
temp->next=NULL;
}
}
void main()
{
int x;
char ch;
clrscr();
printf("\nEnter elements in list 1:\n");
do
{
printf("\nEnter a value: ");
scanf("%d",&x);
insert(x);
fflush(stdin);
display();
printf("\nDo you want to contiune(Y/N):");
scanf("%c",&ch);

}while(ch=='y' || ch=='Y');
printf("\nElements in list 1:\n");
display();
printf("\nEnter elements in list 2:\n");
do
{
printf("\nEnter a value: ");
scanf("%d",&x);
insert2(x);
fflush(stdin);
display2();
printf("\nDo you want to contiune(Y/N):");
scanf("%c",&ch);

}while(ch=='y' || ch=='Y');
printf("\nElements in list 2:\n");
display2();
merge();
printf("\nList after applying merge sort:\n")
display3();
getch();
}