c语言链表动态分配语句问题

请问下为什么动态分配的语句处报一下错误：
implicite declaration of function 'int malloc(...)'

/*
已知一个包含有n个节点的单项环形链表，
编写函数，查找链表中num成员数值最小的
节点，输出该结点的num成员。
*/
#include <string.h>
#include <stdio.h>
struct node{
    int num;
    struct node *next;
}*head;
int search(struct node *p){
    int min = p->num;
    while(p->next != head){
        if((++p)->num < min)
            min = p->num;
    }
    return min;
}
int main(){
    int n = 0,num;
    struct node *p1,*p2;
    p1 = p2 = (struct node*)malloc(sizeof(struct node));
    scanf("%d",&p1->num);
    while(p1->num != 0){
        n++;
        if(n == 1)  head = p1;
        else    p2->next = p1;
        p2 = p1;
        p1 = (struct node*)malloc(sizeof(struct node));
        scanf("%d",&p1->num);
    }
    p2->next = head;
    num = search(head + 1);
    printf("%d\n",num);
    return 0;
} 

缺少头文件。。。，，，，，，，
#include
另外你while都没有个限制，输出的最小值都是0

加上 #incude <stdlib.h>

while(p->next != head)这句没弄懂，这是把下一节点的指针变量与一个类型做判断吗？

#include要加上

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
typedef struct node{
    int num;
    struct node *next;
}*NODE;
NODE head;
int search(NODE p){
    int min = p->num;
    //printf("%d*\n",min);
    while(p->next != head){
        if(p->num < min){
            min = p->num;
        }
        p = p->next;
    }
    printf("%d**\n",min);
    return min;
}
void show(NODE n){
    while(n->next != head){
        printf("%d*",n->num);
        n = n->next;
    }

}
int main(){
    int n = 0;
    NODE p1,p2;
    p1 = p2 = (NODE)malloc(sizeof(NODE));
    head = p1;
    scanf("%d",&p1->num);
    while(p1->num != 9999){
        n++;
        if(n == 1)  p2 = head;
        else{
            p1 = (NODE)malloc(sizeof(NODE));
            scanf("%d",&p1->num);
            p2->next = p1;
            p2 = p1;
            p2->next = head;
        }

    }
    //show(head);
    search(head);
    return 0;
}