Unexpected '%' appearing in console

Question

I'm working through the K&R C programming book, and I just completed exercise 1-13 where you print a histogram of the lengths of words that are input. My horizontal histogram is fine, but my vertical histogram has a '%' sign appearing at the end of it, and I can't figure out why that keeps happening. Here is the loop that I think is causing the issue:

for (i = 0; i < array_length; i++) {
    printf("%-4d", i + 1);
}

If the array_length is 7, I will have a '%' sign after the 7th position like this:

                |           
                |   |       
                |   |       
                |   |       
                |   |       
                |   |       
|   |   |       |   |       
|   |   |   |   |   |       
|   |   |   |   |   |   |   
|   |   |   |   |   |   |   
|   |   |   |   |   |   |   
1   2   3   4   5   6   7   % 

If I remove this loop, the vertical bars print fine, I just don't get the numbering below each of them.

What is going on here? As far as I can guess, the printf is running one extra time with garbage data in 'i', but I can't figure out why or how this is happening.

I'm compiling with gcc on Ubuntu, if that makes any difference.

Here is the complete code for your reference:

#include <stdio.h>

#define IN  1
#define OUT 0
#define ARRAY_SIZE 1000

int main() {

  int c, current_word_length, state, i, j, current_word, largest, array_length, top;
  int word_lengths[ARRAY_SIZE];

  current_word_length = current_word = largest = 0;
  state = OUT;

  for (i = 0; i < ARRAY_SIZE; i++) {
    word_lengths[i] = 0;
  }

  printf("Enter up to 1000 words and this program will calculate their length.\n");
  printf("Please enter a newline, tab, or space before the last word entered, then EOF to print summary.\n\n");

  while ((c = getchar()) != EOF) {

    if (c == ' ' || c == '\t' || c == '\n') {
      if (state == IN) {
        word_lengths[current_word++] = current_word_length;
        if (current_word_length > largest) {
          largest = current_word_length;
        }
        current_word_length = 0;
        state = OUT;
      }
    } else {
      state = IN;
      current_word_length++;
    }

  }

  array_length = current_word;

  printf("\nWord Lengths Histogram Horizontal:\n\n");

  for (i = 0; i < array_length; i++) {
    printf("%-4d: ", i + 1);
    for (j = 0; j < word_lengths[i]; j++) {
      printf("=");
    }
    printf("\n");
  }

  printf("\nWord Lengths Histogram Vertical:\n\n");

  top = largest;

  while (top > 0) {

    for (i = 0; i < array_length; i++) {
      if (word_lengths[i] >= top) {
        printf("%-4c", '|');
      } else {
        printf("%-4c", ' ');
      }
    }

    printf("\n");

    top--;
  }

  for (i = 0; i < array_length; i++) {
    printf("%-4d", i + 1);
  }

  return 0;
}

And here is what I expect to occur using this input string "Bacon ipsum dolor amet frankfurter landjaeger ham":

Enter up to 1000 words and this program will calculate their length.
Please enter a newline, tab, or space before the last word entered, then EOF to print summary.

Bacon ipsum dolor amet frankfurter landjaeger ham

Word Lengths Histogram Horizontal:

1   : =====
2   : =====
3   : =====
4   : ====
5   : ===========
6   : ==========
7   : ===

Word Lengths Histogram Vertical:

                |           
                |   |       
                |   |       
                |   |       
                |   |       
                |   |       
|   |   |       |   |       
|   |   |   |   |   |       
|   |   |   |   |   |   |   
|   |   |   |   |   |   |   
|   |   |   |   |   |   |   
1   2   3   4   5   6   7

Answer 1

OK, as pointed out by nos and chqrlie in the comments, I need to add a newline at the end of my program so that the shell prompt will appear on a newline AFTER the program has finished running.

Adding the putchar() call at the end of main() fixed my issue:

  for (i = 0; i < array_length; i++) {
    printf("%-4d", i + 1);
  }

  putchar('\n');

  return 0;
} // end main()