创建单链表

#include <stdio.h>
#include <stdlib.h>

#define	FALSE	0
#define TRUE	1
typedef struct NODE
{
	struct Node * link;
	int value;
}Node;
//头指针
Node *root = NULL;
//创建链表
Node *createNode(){
	int num = 5;
	int i = 0;
	Node *head = NULL;
	Node *current = NULL;
	Node *previous = NULL;
	
    //自己写的
	// for(;i < num; i++){	    
		// if(0 == i){
		    // current = (Node *)malloc(sizeof(Node));
			// if(current != NULL){
				// head = current;
				// head->value = i * 2; 	
			// }
		// }
		// else{
			// if(i == num - 1){
				// current ->link = NULL;
			// }
			// previous = current;
			// current = (Node *)malloc(sizeof(Node));
			// if(current != NULL){
				// previous->link = current;
				// current->value = i * 2;
			// }	
	
		    
		// }
	// }
	//第二种方法
	head = (Node *)malloc(sizeof(Node));
	if(head == NULL){
		printf("error\n");
		exit(1);
	}
	Node *pTail = head;
	pTail -> link = NULL;
	for(;i < num; i++){	
		Node *new = (Node *)malloc(sizeof(Node));
		if(new == NULL){
			printf("error\n");
			exit(1);
		}
		new ->value = i * 2;
		printf("I : %d\n",i);
		pTail->link = new;
		new ->link = NULL;
		pTail = new;
	}
	return head;
}
//遍历链表
void printTheNode(Node *begin){
	Node *current = NULL;
	current = begin->link;//曾经出错，头结点是没有数据的，所以遍历要从第二个开始
	while(current != NULL){
		printf("the node is :%d \n",current->value);
		current = current->link;
	}
	
}

//插入数值为insertNum的结点
Node *insertMyNum(int insertNum,Node **root){
    Node *current ;
    Node *previous ;
	Node *new ;
	current = *root;
	previous = NULL;
	while(current != NULL && insertNum > current->value  ){
	//while( insertNum > current->value ¤t != NULL )会出错，因为先计算第一个计算式，而第一个在current为NULL的时候就出错了
		previous = current;
		current = current ->link;
	}

	new = (Node *)malloc(sizeof(Node)); 
	if(new ==NULL)
		return NULL;
	new ->value = insertNum;
	
	if(previous == NULL){
		*root = new;
		new ->link = current;
	}	
	// if(current->link  == NULL){
		// current ->link = new;
		// new->link - NULL;
	// }
	else{	
		previous->link = new;
	}	
		
	return *root;
}


//主函数
int main()
{
	int insertNum = 0;
	printf("begin \n");
	root = createNode();
	printTheNode(root);
	printf("end \n");
	printf("input the num you want to insert: \n");
	scanf(" %d",&insertNum);
	root = insertMyNum(insertNum,&root);
	// sll_insert(&root,insertNum);
	printTheNode(root);
	return 1;
}