binary tree를 이용하여 출현 회수를 나타내는 함수 질문!

#include    <stdio.h>
#include    <ctype.h>
#include    <string.h>
#include    "binTree-28.h"
 
#define     MAXWORD     100
 
struct key {
    char    *word;
    int     count;
} keytab[] = {
    { "auto",       0 },
    { "break",      0 },
    { "case",       0 },
    { "char",       0 },
    { "const",      0 },
    { "continue",   0 },
    { "default",    0 },
    { "do",         0 },
    { "double",     0 },
    { "else",       0 },
    { "enum",       0 },
    { "extern",     0 },
    { "float",      0 },
    { "for",        0 },
    { "goto",       0 },
    { "if",         0 },
    { "int",        0 },
    { "long",       0 },
    { "register",   0 },
    { "return",     0 },
    { "short",      0 },
    { "signed",     0 },
    { "sizeof",     0 },
    { "static",     0 },
    { "struct",     0 },
    { "switch",     0 },
    { "typedef",    0 },
    { "union",      0 },
    { "unsigned",   0 },
    { "void",       0 },
    { "volatile",   0 },
    { "while",      0 }
};
 
#define     NKEYS   (sizeof keytab / sizeof(struct key))
 
int         getWord(char *word, int lim);
struct key  *binSearch(char * word, struct key tab[], int n);
 
int
main(void)
{
    char            word[MAXWORD];
    struct key      *p;
    struct tnode    *root;
 
    root = NULL;
   while(getWord(word, MAXWORD) != EOF) {
      if(isalpha(word[0]) &&   
            (binSearch(word, keytab, NKEYS) == NULL))
          root = addTree(root, word);
   }
   for(p = keytab; p < keytab + NKEYS; p++)
       if(p->count > 0)
           printf("%4d %s\n", p->count, p->word);
   treePrint(root);
 
   return 0;
}
 
struct key *
binSearch(char *word, struct key tab[], int n)
{
    struct key *low = &tab[0];
    struct key *high = &tab[n];
    struct key *mid;
    int         cond;
 
    while(low < high) {
        mid = low + (high - low) / 2;
        if((cond = strcmp(word, mid->word)) < 0) high = mid;
        else if(cond > 0) low = mid + 1;
        else return mid;
    } 
 
    return NULL;
}