Thread: c linked list question.

I have the following question. My code is given below. Two problems I'm having with is:
1.How can I link the alphabets without using the arrays? Maybe use a for loop?
2.How to reverse the order of the linked list

Using the following struct:
typedef char DATA;
struct node
{
DATA d;
struct node * next;
};

Write a program to build a single linked list using a loop. Your list should be ordered so
that the last item added is at the beginning of the list

note: I did not use typedef in my code as I'm new to structures and it just confuses me at the moment

Code:

#include <stdio.h>
#include <stdlib.h>	/*for malloc()*/
#include <string.h>

int main()

{
	struct node{
	char d[2];
	struct node *next;			/*pointer to next structure*/
	};

	char *node[26]={"A","B","C","D","E","F",
					"G","H","I","J","K","L",
					"M","N","O","P","Q","R",
					"S","T","U","V","W","X",
					"Y","Z"};

	struct node *first_item;		/*pointer first_item to first structure*/
	struct node *current_item;
	struct node *new_item;
	int index=0;

	/*allocating memory for first structure*/
	first_item=(struct node*)malloc(sizeof(struct node));
	
	/*creating first structure*/
	current_item=first_item;

	/*fill the structures*/
	while(index<26)
	{
	strcpy(current_item->d,node[index]);

	index++;
	
	if (index<26)
		{

		new_item=(struct node*)malloc(sizeof(struct node));
		current_item->next=new_item;		/*set the address of new_item to pointer next*/
		current_item=new_item;
		}
	else
		{
		current_item->next=NULL;
		break;
		}
	
	}

	/*display the results*/

	current_item=first_item;
	index=1;
	while(current_item)
	{
		printf("Structure %d: ",index++);
		printf("%s\n",current_item->d);
		current_item=current_item->next;
	}



	getchar();
	return(0);
}

Originally Posted by bos1234

1.How can I link the alphabets without using the arrays? Maybe use a for loop?

For ASCII, which is almost certainly what you want, the letter 'A' has a decimal value of 65. The letter 'B' is 66, 'C' is 67etc. That means 'B' = 'A' + 1, 'C' = 'A' + 2, etc. The character literals 'A', 'B', 'C', etc are just another way to say 65, 66, 67 in a C program. So you can use a loop to add a number to the letter 'A' and store it in each list node.

2.How to reverse the order of the linked list

The general idea is to traverse the list front to back, popping the first node off and sticking it on the front of a new list. You don't actually need two separate lists though, if you don't care about preserving the original list. To clarify, you have the list A..Z. First you remove the A, and stick it into an empty list. Then the B is in front. You remove that and stick it in front of the A. Then, remove the C from the front of the old list and stick it on the front of the new list. Keep doing this until the original list is empty.

Originally Posted by bos1234

2.How to reverse the order of the linked list

Why are you trying to reverse the array? Just store the new nodes at the beginning of the list as you create them. It's actually easier than storing new nodes at the end. (node->next = list; list = node; )