List Homework
September 7, 2018
For many students, school started a few weeks ago, so today’s exercise is typical of homework:
- Write a program to determine the length of a linked list.
- Write a program to reverse a linked list.
Your task is to write the two list exercises described above; write them as if you are three weeks into your first data structures class. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.
Programming Praxis 
Here’s a solution in C.
#include <stdio.h> #include <stdlib.h> typedef struct node { int value; struct node* next; } node_t; void reverse(node_t** list) { node_t* prev = NULL; node_t* node = NULL; node_t* next = *list; while (next != NULL) { prev = node; node = next; next = next->next; node->next = prev; } *list = node; } size_t length(node_t* list) { size_t result = 0; node_t* node = list; while (node != NULL) { ++result; node = node->next; } return result; } void print_list(node_t* list) { node_t* node = list; printf("{"); while (node != NULL) { printf("%d", node->value); node = node->next; if (node) printf("->"); } printf("}"); } int main(int argc, char* argv[]) { node_t* list = NULL; for (int i = argc - 1; i > 0; --i) { node_t* node = (node_t*)malloc(sizeof(node_t)); node->next = list; node->value = atoi(argv[i]); list = node; } printf("list:\n "); print_list(list); printf("\n"); size_t len = length(list); printf("len(list):\n %zu\n", len); reverse(&list); printf("reverse(list):\n "); print_list(list); printf("\n"); node_t* node = list; while (node != NULL) { node_t* next = node->next; free(node); node = next; } return EXIT_SUCCESS; }Example Usage:
$ ./a.out {1..10} list: {1->2->3->4->5->6->7->8->9->10} len(list): 10 reverse(list): {10->9->8->7->6->5->4->3->2->1}