CTDL&TT: Danh sách dùng mảng

#include <stdio.h>
#include <conio.h>
#define maxlength 1000

typedef int elementtype;
typedef struct list_tag{
    elementtype elements[maxlength];
    int last;
}list_type;

list_type ds;

void create(list_type *lp){
    lp->last = -1;
}

int end(list_type *lp){
    return (lp->last+1);
}

void insert(elementtype x, int p, list_type *lp){
    int i;

    if(lp->last >= maxlength-1){
        printf("List is full!");
        return;
    }

    if ((p<0) || (p>lp->last+1)) {
        printf("Position doesnot exist!");
        return;
    }

    for (i=lp->last; i>= p; i--){
        lp->elements[i+1] = lp->elements[i];
    }
    lp->elements[p] = x;
    lp->last++;
}

void del(int p, list_type *lp){
    int i;
    if ((p<0) || (p>lp->last)) {
        printf("Position does not exist!\n");
    }
    lp->last--;
    for (i=p; i <= lp->last; i++){
        lp->elements[i+1] = lp->elements[i];
    }
}

int locate(elementtype x, list_type *lp){
    int i;
    for (i = 0; i <= lp->last; i++){
        if (lp->elements[i] == x){
            return i;
        } else return -1;
    }
}

int retrieve(int p, list_type *lp){
    if (p<0 || p>lp->last){
        printf("Position does not exist!! \n");
        return;
    }

    return lp->elements[p];
}

int next(int p, list_type *lp){
    if (p<0 || p>lp->last-1){
        printf("Position does not exist!! \n");
        return;
    }

    return lp->elements[p+1];
}

int prev(int p, list_type *lp){
    if (p<1 || p>lp->last){
        printf("Position does not exist!! \n");
        return;
    }

    return lp->elements[p-1];
}



void printds(list_type *lp){
    int i;
    printf("Danh sach %d phan tu: \n", lp->last+1);
    for (i = 0; i <= lp->last; i++){
        printf("%d", lp->elements[i]);
        printf(" ");
    }
    printf("\n\n");
}

void main(){
    create(&ds);
    insert(12,0,&ds);
    printds(&ds);
    insert(6,0,&ds);
    insert(16,0,&ds);
    insert(9,0,&ds);
    insert(7,2,&ds);
    insert(23,3,&ds);
    insert(3,1,&ds);
    insert(40,3,&ds);
    printds(&ds);
    int a = retrieve(4, &ds);
    printf("%d", a);

}