C Academy · Lesson

Traversal and Search

Walk the list.

Walking the list

Traversal means visiting each node in order. You start at the head and follow next pointers until you reach NULL.

Almost every list algorithm builds on this simple walk.

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

struct Node { int value; struct Node *next; };
struct Node *make(int v){struct Node*n=malloc(sizeof*n);n->value=v;n->next=NULL;return n;}

int main(void) {
    struct Node *head = make(10);
    head->next = make(20);
    for (struct Node *p = head; p != NULL; p = p->next)
        printf("%d ", p->value);
    printf("\n");
    return 0;
}

The traversal pattern

The canonical loop uses a moving pointer p: initialize it to head, continue while p is not NULL, and advance with p = p->next.

Never modify head itself while walking, or you lose the start of the list.

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

struct Node { int value; struct Node *next; };
struct Node *make(int v){struct Node*n=malloc(sizeof*n);n->value=v;n->next=NULL;return n;}

int main(void) {
    struct Node *head = make(1);
    head->next = make(2);
    struct Node *p = head;
    while (p) { printf("%d ", p->value); p = p->next; }
    printf("\n");
    return 0;
}

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