CODEWITHSUNDEEP
clinked-list
Xavier
Xavier

Reputation: 119

Linked list only prints the first value of first list

I have a program where three values are inserted into linked lists. When I try to iterate through the list I only get the first value printed. Sorry if the function names are confusing I'm still new to c and I'm trying to use the function and variable names gave me just to make my life easier when taking a test. I'm also pretty unfamiliar with debugger and how I would use it to find out what is going on here. Thanks in advance.

void program_header(char i[]);
Node *allocateNode(int iNewInfo);
Node *searchLL(Node *pHead, int iMatch, Node **ppPrecedes);
Node *insertLL(Node **ppHead, int iNewInfo);
void printLL(Node *pHead);

int main(int argc, char *argv[])
{   
    program_header(argv[0]);
    insertLL(&pHead, 84);
    insertLL(&pHead, 45);
    insertLL(&pHead, 81);
    printLL(pHead);

    return 0;
}

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

typedef struct Node
{
    int iInfo;
    struct Node *pNext;
}Node;

Node *pHead = NULL;
Node *pNew  = NULL;
Node *pPrecedes = NULL;

Node *allocateNode(int iNewInfo)
{
    // to allocate a new node
    pNew = malloc(sizeof(Node));
    if (pNew == NULL)
        printf("Memory allocation error");
        pNew->iInfo = iNewInfo;
        pNew->pNext = NULL;
    return pNew;
}

Node *searchLL(Node *pHead, int iMatch, Node **ppPrecedes)
{
Node *p;
for (p = pHead; p != NULL; p = p->pNext)
{
if (iMatch == p->iInfo)
    printf("Found! %d\n", iMatch);
    return p;
    if (iMatch < p->iInfo)
        return NULL;
    *ppPrecedes = p;
}
return NULL;
}

Node *insertLL(Node **ppHead, int iNewInfo)
{

Node *pFind;    
// see if it already exists
pFind = searchLL(*ppHead, iNewInfo, &pPrecedes);
if(pFind != NULL)
   return pFind;

// Doesn't already exist.  Allocate a node and insert it
pNew = allocateNode(iNewInfo);
if(pPrecedes == NULL)
{     //insert at head
      pNew->pNext = *ppHead;
      *ppHead = pNew;
}
else
{     //insert after a node
      pNew->pNext = pPrecedes->pNext;
      pPrecedes->pNext = pNew;
}
return pNew; 
}

void printLL(Node *pHead)
{
    Node *p;
    printf("iInfo Values\n");
    for (p = pHead; p != NULL; p = p->pNext)
    {
        printf("%d\n", p->iInfo);
    }
        p = pHead;
}

void program_header(char i[])
{   

    int j, n = strlen(&i[2]);
    char *name = &i[2], border[n], dash = '-';

    // loads dashes into array
    for(j = 0; j < n; j++)
        border[j] = dash;
    border[j] = '\0';

    // print header
    printf("\n~%s~\n~%s~\n~%s~\n\n"
        , border, name, border);
}

Upvotes: 0

Views: 94

Answers (2)

pstrjds
pstrjds

Reputation: 17428

I believe your problem is in your search method. I have reformatted it to show the way that it is currently behaving. To help in making your code more readable and to avoid these type of errors you should get in the habit of using braces in your if statements even if they are only one line.

This is your current code

Node *searchLL(Node *pHead, int iMatch, Node **ppPrecedes)
{
    Node *p;
    for (p = pHead; p != NULL; p = p->pNext)
    {
        if (iMatch == p->iInfo)
        {
            printf("Found! %d\n", iMatch);
        }

        return p;

        if (iMatch < p->iInfo)
        {
            return NULL;
        }
        *ppPrecedes = p;
    }
    return NULL;
}

Notice in the for loop that no matter if a match is found or not you are always returning p which is really pHead. Then in your insert code you are checking to see if the item is found in the list. Since you always return head it thinks that the item is in the list and never adds a new item.

I haven't tested this, but I believe this is the change you would need to make. You are expecting the search to return a node if the value is already in the list. So you want to return p if there is a match, otherwise you want to return NULL: 

Node *searchLL(Node *pHead, int iMatch, Node **ppPrecedes)
{
    Node *p;
    for (p = pHead; p != NULL; p = p->pNext)
    {
        if (iMatch == p->iInfo)
        {
            printf("Found! %d\n", iMatch);
            return p;
        }

        if (iMatch < p->iInfo)
        {
            return NULL;
        }
        *ppPrecedes = p;
    }
    return NULL;
}

Upvotes: 1

milevyo
milevyo

Reputation: 2180

correct this

Node *allocateNode(int iNewInfo)
{
    // to allocate a new node
    pNew = malloc(sizeof(Node));
    if (pNew == NULL)
        printf("Memory allocation error");
        pNew->iInfo = iNewInfo;
        pNew->pNext = NULL;
    return pNew;
}

to this

Node *allocateNode(int iNewInfo)
{
    // to allocate a new node
    pNew = malloc(sizeof(Node));
    if (pNew){
        pNew->iInfo = iNewInfo;
        pNew->pNext = NULL;
   }else{
        printf("Memory allocation error");
   }
    return pNew;
}

Upvotes: 0

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