K&R book exercies 1-13 solution and opinions

Hi all! I'm going through K&R by my own and would like some opinions about my solution to this exercise:

"Write a program to print a histogram of the lengths of words in its input. It is easy to draw the histogram with the bars horizontal; a vertical orientation is more challenging."

Based on the assumptions that a word is any character different than blank space, tab or new line and that I will receive words of maximum 12 characters long, this is my solution:

#include <stdio.h>
#define MAX_WORD_LEN 12  /* max number of chars per word */

int main(void)
{
  int chr;
  int i;
  int word_length;
  int frequencies[MAX_WORD_LEN];

  word_length = 0;

  while ((chr = getchar()) != EOF) {
    if (chr == ' ' || chr == '\t' || chr == '\n') {
      if (word_length > 0) {
        ++frequencies[word_length - 1];
        word_length = 0;
      }
    } else {
      ++word_length;
    }
  }

  /* print results as a histogram */
  for (i = 0; i < MAX_WORD_LEN; ++i) {
    printf("%2d|", i + 1);
    while (frequencies[i]--)
      printf("=");
    printf("\n");
  }

  return 0;
}