Data Structures: Linked List Code

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Simple Linked List

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#include <stdio.h>
 
struct student
{
    long num;
    float score;
    struct student *next;
};
 
void main()
{
    struct student a, b, c, *head, *p;
    a.num = 99101; a.score = 89.5;
    b.num = 99103; b.score = 90;
    c.num = 99107; c.score = 85;  // Assign values to num and score members
    head = &a;  // Assign start address of node a to head pointer
    a.next = &b;  // Assign start address of node b to node a's next member
    b.next = &c;
    c.next = NULL;  // Node c's next member stores no further address
    p = head;  // Point p to node a
    do
    {
        printf("%ld %5.1f\n", p->num, p->score);  // Output data from node pointed to by p
        p = p->next;  // Move p to the next node
    }while(p != NULL);  // p becomes NULL after node c is output
    system("pause");
}

Memory Allocation Functions

malloc function

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void *malloc(unsigned int size);

Allocates a block of memory of length size in the dynamic storage area. The return value is a pointer (type void *) to the starting address of the allocated space. If the function fails (e.g., insufficient memory), it returns a NULL pointer.

calloc function

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void *calloc(unsigned n, unsigned size);

Allocates n continuous blocks of memory, each of length size, in the dynamic storage area. It returns a pointer to the starting address, or NULL if allocation fails. calloc is useful for dynamic arrays, where n is the number of elements and size is the element size.

free function

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void free(void *p);

Releases the memory pointed to by p, making it available for other variables. p must be a value returned by a previous calloc or malloc call. free has no return value. Note: In older C versions, malloc and calloc returned char * pointers; ANSI C defines them as void *.

Implementing a Dynamic Linked List

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#include <stdio.h>
#include <stdlib.h>
 
#define NULL 0
#define LEN sizeof(struct student)

struct student
{
    long num;
    float score;
    struct student *next;
};
 
struct student *create()
{
    struct student *p1, *p2, *head;
    int num;
    float score;
    int n = 0;
 
    head = NULL;
 
    p1 = p2 = (struct student *)malloc(LEN);
 
    printf("please input num and score.\n");
    scanf("%d,%f", &p1->num, &p1->score);
 
    while(p1->num != 0)
    {
        n ++;
        if(n == 1)
            head = p1;
        else
            p2->next = p1;
        p2 = p1;
        p1 = (struct student *)malloc(sizeof(struct student));
 
        printf("please input num and score.\n");
 
        scanf("%d,%f", &p1->num, &p1->score);
    }
    p2->next = NULL;
    return head;
}
 
void printlist(struct student *head)
{
    struct student *p;
    p = head;
    if(head != NULL)
    {
        do
        {
            printf("num=%d score=%f\n", p->num, p->score);
            p = p->next;
        }while(p != NULL);
    }
}
 
void main()
{
    struct student *head;
    head = create();
    printlist(head);
    system("pause");
}

// Print the list
void printlist(struct student *head)
{
    struct student *p;
    p = head;

    if(head != NULL)
    {
        do 
        {
            printf("num=%d score=%5.2f\n", p->num, p->score);
            p = p->next;
        } while (p != NULL);
    }
    /* while(p -> next != NULL)
    {
        printf("num=%d score=%f\n", p->num, p->score);
        p = p->next;
    }*/
}

// Delete a node
struct student *delNode(struct student *head, int num)
{
    printf("delNode.\n");
    struct student *p1, *p2;
    if(head == NULL)
    {
        printf("The List is NULL.\n");
    }
    else
    {
        p1 = head;
        while(p1->next != NULL && p1->num != num)
        {
            p2 = p1;
            p1 = p1->next;
        }
        if(p1->num == num)
        {
            if(p1 == head)
                head = p1->next;
            else
                p2->next = p1->next;
        }
        else
            printf("Can not find list num.\n");
    }
    return head;
}

// Update a node
struct student *update(struct student *head, int index, int num, float score)
{
    printf("update.\n");
    struct student *p;
    if(head == NULL)
    {
        printf("The List is NULL.\n");
    }
    else
    {
        p = head;
        while(p->next != NULL && p->num != index)
        {
            p = p->next;
        }
        if(p->num == index)
        {
            p->num = num;
            p->score = score;
        }
        else
            printf("Can not find list index.\n");
    }
    return head;
}

// Add a node
struct student *add(struct student *head, int index, int num, float score)
{
    printf("add.\n");
    struct student *p1, *p2, *p3;
    if(head == NULL)
    {
        printf("The List is NULL.\n");
    }
    else
    {
        p1 = p2 = head;
        while(p1->next != NULL && p1->num != index)
        {
            p1 = p1->next;
            p2 = p1;
        }
        if(p1->num == index)
        {
            p3 = (struct student *)malloc(LEN);
            p3->num = num;
            p3->score = score;

            if(p2->next == NULL)
            {
                p2->next = p3;
                p3->next = NULL;
            }
            else
            {
                p3->next = p2->next;
                p2->next = p3;   
            }
        }
        else
            printf("Can not find list index.\n");
    }
    return head;
}