K&R "The C Programming Language" exercise 1-13: histograms

Question

Exercise 1-13. 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.

The code I wrote:

#include <stdio.h>
#define MAXWLEN 35 /* assuming no word longer than 35 characters will appear in the input */
#define IN 0
#define OUT 1
int main()
{
 int c, len, longest, state, chart[MAXWLEN];
 for (int i = 0; i < MAXWLEN; ++i)
 chart[i] = 0;
 len = 0; /* length of the current word */
 longest = 0; /* the longest word appearing in the input */
 state = OUT; /* the state of being inside or outside a word */
 while ((c = getchar()) != EOF)
 { 
 if (c == ' ' || c == '\t' || c == '\n')
 {
 if (state == IN)
 if (longest < ++chart[len-1])
 longest = chart[len-1];
 state = OUT;
 len = 0;
 }
 else
 {
 state = IN;
 ++len;
 }
 }
 
 char q[2][3] = {"", " "};
 for (int i = longest; i; --i)
 for (int j = (c = putchar('\n')) - c; j < MAXWLEN; ++j)
 (i <= chart[j]) ? printf(" * ") : printf("%s", q[chart[j] > 0]);
 
 putchar('\n');
 for (int i = 1; i <= MAXWLEN; ++i)
 if(chart[i-1])
 printf("%2d ", i);
 putchar('\n');
 return 0;
}

• J_H: Kernighan didn't ask you to "Write a program which defines several functions", but implicitly you might view it that way. It's always OK to break out helper functions, such as getword().

Answer 1

• for (int j = (c = putchar('\n')) - c; is too clever to be good. You save one line of vertical space by the price of a reviewer's mental effort. Don't do this. Be explicit:

   putchar('\n');
   for (int j = 0; ....)
  

  is much more readable.

  Ditto for

   (i <= chart[j]) ? printf(" * ") : printf("%s", q[chart[j] > 0]);
  

• As said in the comment, more functions please. There are clearly init_chart, fill_chart, and print_chart (every loop deserves to be a function).

  getword is also nice to have. It lets you avoid a IN/OUT state machine.

• c == ' ' || c == '\t' || c == '\n' is insufficient. At least there is \v (vertical tab) and \f (formfeed). Prefer isspace (don't forget to #include <ctype.h>. (I know that it the K&R times it was not available)

• putchar may fail. Be prepared.