Linked list problem

[manutdfan]

I have to write a program which will convert the input:

Hello
World
Test
.

into

Test
World
Hello

I have written a program so far that takes the input and stores it in a linked list, though I am not entirely sure how I can change this into the output. I have been told not to use arrays, the only idea I have is to try to read each line into a seperate list and then swap them over.

Though the problem is with this I don't know how many lines will be entered so I don't know how many lists will need to be created.

I would really appreciate any advice on how I should go about adapting my program to solve this problem.

Thanks in advance

[sl4nted]

the only idea I have is to try to read each line into a seperate list

-- do you mean seperate list node?

if you make a list and just keep adding to the head of the list, they will end up in the order you want

ie.

add Hello
List: Hello
add World
List: World -> Hello
add test
List: test -> World -> Hello

print from head to tail. want the orignal as well? use a doubly linked list and keep points to head and tail so you can traverse in either direction

[manutdfan]

This is the code I have used, it reads each character into a seperate node. How would I change the lines I have (currently seperate nodes) into a single node per line?

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

typedef struct List{
        char x;
        struct List *next;
}list;

list *insertlist(char hd, list *a1){
     list *a = calloc(1,sizeof(list));
     a->x = hd;
     a->next = a1;
     return a;
     free (a);
}

list *mainlist(){
     list *b = NULL;
     char i = 0;
     while (i != '.'){
           i = getchar();
           b = insertlist(i,b);
           }
     return b;
     }
     
int main(){
    list *c = calloc(1,sizeof(list));
    list *temp = NULL, *d = NULL ;
    printf("Please enter the phrase you wish to store in a list: \n");
    d = mainlist();
    
    while(d)
    {
       c = d->next;
       d->next = temp;
       temp = d;
       d = c;
    }
    d = temp;
    
    
    

    if(d != 0) { 
    printf("\n");
    while(d->next != 0) {
        printf("%c", d->x);
        d = d->next;
    }
    printf("%c", d->x);
}
    return 0;    
}

[sl4nted]

typedef struct List{
        char x;
        struct List *next;
}list;

needs to hold a string, so char x[STRINGLENGTH] or char *x

list *insertlist(char hd, list *a1){

needs to take char *hd now
and inside copy the string with strncpy or similar

in mainlist you will take the whole list from the user and put it in a buffer
fgets

that buffer can then be broken up into words deliminated by " "
those words are then used to call the new insertlist

[manutdfan]

Trouble is don't I need to create an array to hold the string which I am not allowed to do.

I have modified my code so it now reads it in reverse order and then tries to switch the first line round, although it doesn't seem to work and I can't understand why.

I would be very grateful if someone could check it over for me, I think the problem is in one of the highlighted areas.

Thanks

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

typedef struct List{
        char x;
        struct List *next;
}list;

list *insertlist(char hd, list *a1){
     list *a = calloc(1,sizeof(list));
     a->x = hd;
     a->next = a1;
     return a;
     free (a);
}

list *mainlist(){
     list *b = NULL;
     char i = 0;
     while (i != '.'){
           i = getchar();
           b = insertlist(i,b);
           }
     return b;
     }

list *lookup(char c, list *head){
     if (head == NULL)
        return NULL;
     else if (c == head->x)
        return head;
     else
         return (lookup(c, head->next));
}
     
list *reversewords(list *a){
     list *b;
     list *temp = NULL;
     list *c = calloc(1,sizeof(list));
     a = a->next;
     a = lookup('\n', a);
     b = b->next;
     b = b->next;
     b = lookup('\n', b);
     
     
     while(a < b)
    {
       c = a->next;
       a->next = temp;
       temp = a;
       a = c;
       a++;
    }
    a = temp;
    
    return a;
}

     
int main(){
    
    list *d = NULL ;
    printf("Please enter the phrase you wish to store in a list: \n");
    d = mainlist();
    d = reversewords(d);

    if(d != 0) { 
    printf("\n");
    while(d->next != 0) {
        printf("%c", d->x);
        d = d->next;
    }
    printf("%c", d->x);
}
    return 0;    
}

[vart]

Why not use the bidirectional linked list. It can be traversed in any direction - no manipulations needed

[manutdfan]

I haven't been taught that yet, so I presume I am supposed to use a normal linked list.

[vart]

your reversewords function has several erros
1. b = b->next;
b is not initialized, possible GPF
2. c = a->next;
previously c was set to allocated memory, now this memory is lost
3. a++; you allocate one node at time, ++ operation can be used only on pointers pointing to arrays
Maybe thre is something else

lookup can be simply done using loop ( no stack overflow possibility)

[sl4nted]

I see, no arrays period. Are you allowed to change that struct?...is so, an easier method would be to just have an int length member, so everytime you see a space you record the length of that word...otherwise say its -1 or 0 or somthin. then it would only take a small recusive function to take in that list and length and print it correctly.

[sl4nted]

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

typedef struct List{
        char x;
        int len;
        struct List *next;
}list;

list *insertlist(char hd, list *a1, int len){
     list *a = calloc(1,sizeof(list));
     a->x = hd;
     a->len = len;
     a->next = a1;
     return a;
     free (a);
}

list *mainlist(){
     list *b = NULL;
     int n = 0;
     char i = 0;

     while (i != '.'){
           i = getchar();
           if ((i == ' ') || (i == '.')) {
                b = insertlist(i,b,n);
                n = 0;
           }
           else
           {
               b = insertlist(i,b,0);
               n++;
           }
     }
     return b;
}

void print_word(list *l, int i)
{
   if (i != 0)
       print_word(l->next, i-1);

   if (l->x == '.')
       printf(" ");
   else printf("%c", l->x);
}

int main(){

    list *d = NULL ;
    list *temp;

    printf("Please enter the phrase you wish to store in a list: \n");
    d = mainlist();

    temp = d;
    if(temp != 0) {
    printf("\n");

    while(temp->next != 0) {
        if (temp->len != 0)
        {
            print_word(temp, temp->len);
        }
        temp = temp->next;
    }
    printf("\n");

    }
    return 0;
}

heres POC based on your code

output:
Please enter the phrase you wish to store in a list:
Hello World Test.

Test World Hello

edit::
another output
Please enter the phrase you wish to store in a list:
This is a LONGER better testing phrase.

phrase testing better LONGER a is This

[manutdfan]

Thanks for the help, though it doesnt seem to work.

The code below is my last update, I have no got it to print the last word first. Although the list is no longer linked together so I cannot figure out how to reverse the other words in the list.

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

typedef struct List{
        char x;
        struct List *next;
}list;

list *insertlist(char hd, list *a1){
     list *a = calloc(1,sizeof(list));
     a->x = hd;
     a->next = a1;
     return a;
     free (a);
}

list *mainlist(){
     list *b = NULL;
     char i = 0;
     b = insertlist('\n',b);
     while (i != '.'){
           i = getchar();
           b = insertlist(i,b);
           }
     
     return b;
     }

list *lookup(char c, list *head){
     if (head == NULL)
        return NULL;
     while (head->x != c){
           head = head -> next;
     }
     return head;

     
}
     
list *reversewords(list *a,list *b){
     list *temp = NULL;
     list *c = calloc(1,sizeof(list));
   
     a = a->next;
     a = lookup('\n', a);
     b = b->next;
     b = b->next;
     b = lookup('\n', b);
     
     
     while(a != b)
    {
       c = a->next;
       a->next = temp;
       temp = a;
       a = c;
       
    }
    a = temp;
    
     
    
        
    return a;
}

     
int main(){
    
    list *d = NULL ;
    printf("Please enter the phrase you wish to store in a list: \n");
    d = mainlist();
    d = reversewords(d,d);

    if(d != 0) { 
    printf("\n");
    while(d->next != 0) {
        printf("%c", d->x);
        d = d->next;
    }
    printf("%c", d->x);
}
    return 0;    
}

[vart]

you still have a problem with loosing pointer to allocated memory and using uninitialized pointer (now it is a)