🚀 go-pugleaf

you@matt.ksu.ksu.edu writes:

>Hello,
>  I'm playing with C++, teaching it to myself.  What I would like to know how to
>do is reference certain pointers in a weird way....let me explain.  I'm
>using a trie ADT.  Each node has 27 children, A-Z plus one to see if it's a word
>or not.  It's a type of spell checker.  You trace down the tree the letters of
>the word and when you're done, you check to see if it's a valid word or not.  
>Of course, if along that way you find a path is NULL then it isn't a word.  What
>I had hoped could be done is something like this, where the word is in the
>variable "inword":
>
>	char1 = toupper(inword[count]);
>	if (dictionary->char1==NULL)
>		notfound=1;
>	else
>		dictionary=dictionary->char1;
>
>Count keeps tract of which letter the program is searching for and when count
>equals the length of the word, you check to see if the flag is set and if
>it is, then it's a word, else it isn't.  I've looked at the enum datatype
>but I haven't had any luck with it.  Any help would be greatly
>appreciated.  What I don't want to do is this:
>
>      switch(*char1) {
>         case 'A' : {
>            if (current->a==NULL)
>               done = 1;
>            else
>               current=current->a;
>            };
>         case 'B' : {
>            if (current->a==NULL)
>               done = 1;
>            else
>               current=current->b;
>            };
>         case 'C' : {
>            if (current->c==NULL)
>               done = 1;
>            else
>               current=current->c;
>            };
>.......
>
>					Thanks, 
>						Kevin

Use an array of pointers:

struct trie {
	int is_word;
	struct trie *next[26];
} *dictionary;	/* you better initialize this yourself! */

/* return TRUE if inword is in dictionary */
int check_word(const char *inword) {
	const struct trie *ptr;
	int index, c;
	for (ptr=dictionary; ptr && *inword; ptr=ptr->next[index]) {
		assert(isalpha(*inword));
		c = toupper(*inword++);
		index = c - 'A';  /* works for ASCII but not for EBCDIC */
		assert(0<=index && index<26
	}
	return ptr && ptr->is_word;
}
-- 
Fergus Henderson             fjh@munta.cs.mu.OZ.AU      
This .signature VIRUS is a self-referential statement that is true - but 
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-- 
Fergus Henderson             fjh@munta.cs.mu.OZ.AU      
This .signature VIRUS is a self-referential statement that is true - but 
you will only be able to consistently believe it if you copy it to your own
.signature file!