รบกวน ดูโค้ดและ อธิบาย สอน ตัวอย่างนี้ที่ครับว่าผิดยังไง บ้าง

#include <stdio.h>
struct node {
	int data;
	struct node *next;
	struct node *back;
};
void AddNode(struct node **walk);
////////////////////////
void SwapNode2(struct node **begin,struct node *walk1,struct node *walk2);  //<<<<---- วิธีประกาศ เราสามารถรู้ได้อย่างไรว่าต้องประกาศอะไร
////////////////////////
int main()
{
	int i,n,g1,g2,value;
	struct node *start,*now,*now2;
	start=NULL;
	scanf("%d",&n); //how many nodes?
	for(i=0; i<n; i++) 
		AddNode(&start);	
	scanf("%d %d",&g1,&g2); //go to node?
	while(g1>=0 && g1<n && g2>=0 && g2<n) {
		now=start;
		for(i=0; i<g1 && now!=NULL; i++) 
			now=now->next;		
		now2=start;
		for(i=0; i<g2 && now2!=NULL; i++) 
			now2=now2->next;		
		SwapNode2(&start,now,now2);
		now=start;
		printf("Swap node %d,%d", g1, g2);
		printf("\nList forward: ");
		while(now!=NULL) { //show all from start node
			printf("%d ",now->data);
			if(now->next!=NULL) now=now->next;	
			else break; //go last node, ready to show backward
		}
		printf("\nList backward: ");
		while(now!=NULL) { //show all from last node
			printf("%d ",now->data);
			now=now->back;	
		}
		printf("\n");
		scanf("%d %d",&g1,&g2); //go to node?
	}
	return 0;	
}
void AddNode(struct node **walk)
{
	struct node *temp;
	temp=NULL;
	while(*walk!=NULL) {
		temp=*walk; 
		walk=&(*walk)->next; 
	}
	*walk=new struct node; 
	scanf("%d",&(*walk)->data);
	(*walk)->next=NULL; 
	(*walk)->back=temp; 
}
////////////////////////
void SwapNode2(struct node **begin,struct node *walk1,struct node *walk2){
	struct node *temp;
		if((walk1)->back==NULL)
			*begin = walk2;
		else
			walk1->back->next = walk2;	//----(1)
		if((walk2)->back==NULL)
			*begin = walk1;
		else
			walk2->back->next = walk1;	//----(2)
		temp = walk1->next;				//----(3)
		walk1->next = walk2->next;		//----(4)
		walk2->next = temp;				//----(5)
		temp = walk2->next;				//----(6)
		walk2->back = walk1->back;		//----(7)
		walk1->back = temp;			//----(8)
		if((walk1)->next!=NULL){
			walk1->next->back=walk1;	//----(9)
		}
		if((walk2)->next!=NULL){
			walk2->next->back=walk2;	//----(10)
		}
}
////////////////////////