c programming language

the code so far had warnings and doesnt seem to perform correctly . please if you could explain what i have wrong . thanks .

#include

#include

struct listNode

{

int data;

struct listNode* nextPtr;

};

typedef struct listNode node;

void insert (node *);

void showList(node *);

node *merge(node*,node*);

int main (void)

{

int choose;

node*list1,*list2;

{

printf(" choose and enter: ");

printf(" 1. first list ");

printf(" 2. second list ");

printf(" 3. merge two list ");

printf(" 4. exit ");

printf(" ? ");

scanf("%d",&choose );

switch (choose)

{

case 1 :

printf(" enter values for first list(0 to end):");

list1 = (node *)malloc(sizeof(node *));

insert(list1);

printf(" list1 = ");

showList(list1);

break;

case 2:

printf(" values for second list(0 to end): ");

list2= (node*)malloc(sizeof(node*));

insert(list2);

printf(" list 2 = ");

showList(list2);

break;

case 3:

printf(" after merge:");

list1= merge(list1,list2);

printf("merged list is :");

showList(list1);

break;

case 4 :

break;

default:

printf(" enter choice! ");

break;

}

}while (choose !=4);

return (0);

}

void insert (node*list)

{

printf(" enter value:");

scanf("%d", &list->data);

if (list->data == 0 )

{

(list->nextPtr);

}

else

{

list->nextPtr= (node*)malloc(sizeof(node));

insert (list->nextPtr);

}

}

void showList (node* list)

{

node*p;

for(p=list;p->nextPtr != NULL; p=p-> nextPtr)

printf("%d",p->data);

if (list->nextPtr==NULL)

{

printf(" list is empty ");

}

}

node* merge(node*list1,node *list2)

{

node mergeList;

node*temp=&mergeList;

while (list1->nextPtr != NULL && list2 ->nextPtr->nextPtr !=NULL)

{

if (list1->datadata)

{

temp->nextPtr=list1;

list1= list1->nextPtr;

}

else

{

temp->nextPtr=list2;

list2=list2->nextPtr;

}

temp=temp->nextPtr;

}

if (list1 ->nextPtr == NULL)

temp->nextPtr= list2;

if (list2->nextPtr->nextPtr==NULL)

temp->nextPtr = list1;

return mergeList.nextPtr;

}

12.7 (Merging Ordered Lists) Write a program that merges two ordered lists of integers into a single ordered list of integers. Function merge should receive pointers to the first node of each of the lists to be merged and return a pointer to the first node of the merged list