Uninitialized values in trie

Question

I just implemented a trie in c, ran valgrind on my program and although all heaps were freed, it says something about uninitialized values. Here's Valgrind's output http://pastebin.com/7hSWGiDk

And here is trie code(In the trie's typedef, the array has 26 elements for English letters, 1 element for apostrophe and 1 element which when not null, marks the end of word) :

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

typedef struct trie
{
    struct trie* array[28];
} trie;


void add(char* word, trie* start)
{
    trie* current = start;
    trie* previous = NULL;
    int i = 0;

    while(current!=NULL && i < strlen(word))
    {
        previous = current;
        current = current->array[word[i] - 'a'];  
        i++;      
    }
    i--;
    for(;i < strlen(word);i++)
    {
            previous->array[word[i] - 'a'] = malloc(sizeof(trie));
            previous = previous->array[word[i] - 'a'];
    }
    previous->array[27] = malloc(sizeof(trie));     
}

bool search(char* word, trie* start)
{
    trie* current = start; 
    for(int i = 0;i < strlen(word);i++)
    {
        current = current->array[*(word+i) - 'a'];
        if(current == NULL)
        {
            return false;
        }
    }
    if(current->array[27]!=NULL)
    {
        return true;
    }
    return false;
}

void clear(trie* start)
{
    if(start != NULL)
    {
        for(int i = 0;i < 28;i++)
        {
            clear(start->array[i]);
        }
        free(start);
    }
}

int main(void)
{
    trie* start = malloc(sizeof(trie));
    char* word = "ba\0";
    add(word,start);
    clear(start);
}

Answer 1

When you create start node you leave array members uninitialized , but later in add function you operate on them. For the first time in this line

current = current->array[word[i] - 'a'];  

I think following should solve the issue :

trie* start = malloc(sizeof(trie));
for(int i = 0; i < 28; ++i)
{
   start->array[i]=NULL;
}