Question 4 of 9: File I/O — Lines and Words per Line

Question 4: File I/O — Lines and Words per Line (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Given. A text file whose lines hold at most 256 characters each, and whose word boundaries are exactly four delimiter kinds: blank, comma, period, and line start/end.

Find. The total number of lines, and the number of words in each individual line.

Approach. Read the file one line at a time; for each line, scan character by character maintaining an "in a word" flag that starts a new word count whenever a non-delimiter follows a delimiter (or the start of line), so each line's word count falls out of a single forward scan with no need to store the words themselves.

1. Write the per-line scan and accumulate a line count.

   #include <stdio.h>
   
   #define MAXLINE 258   /* 256 chars + '\n' + '\0', per the stated line bound */
   
   int is_delim(int c) { return c == ' ' || c == ',' || c == '.'; }
   
   int count_words(const char *line)
   {
       int count = 0, in_word = 0;
       for (; *line != '\0' && *line != '\n'; line++) {
           if (is_delim((unsigned char) *line)) {
               in_word = 0;
           } else if (!in_word) {
               in_word = 1;
               count++;
           }
       }
       return count;
   }
   
   int main(void)
   {
       char filename[256], line[MAXLINE];
       FILE *fp;
       long nlines = 0;
   
       printf("Enter file name: ");
       if (scanf("%255s", filename) != 1) return 1;
   
       fp = fopen(filename, "r");
       if (fp == NULL) { printf("Could not open %s\n", filename); return 1; }
   
       while (fgets(line, MAXLINE, fp) != NULL) {
           nlines++;
           printf("Line %ld: %d word(s)\n", nlines, count_words(line));
       }
       printf("Total lines: %ld\n", nlines);
   
       fclose(fp);
       return 0;
   }

2. Trace it on a worked example file of three lines: "Hello, world. This is fun.", "One more line here", "Last one.". Line 1 has words Hello / world / This / is / fun (the comma and period act as delimiters exactly like a blank, so "Hello," splits into "Hello" plus a delimiter, not a 6-character token) — 5 words. Line 2 has 4 words (no punctuation, blanks only). Line 3 has 2 words (Last, one). $$\boxed{\text{lines}=3,\ \text{words per line}=(5,4,2)}$$