Week 1

TA: Francis Hsu
Email: fahsu@ucdavis.edu
Website: http://wwwcsif.cs.ucdavis.edu/~hsuf/ecs40
Office Hours: 53 Kemper Tu 3:30-5:30, Th 10-12

words.c 

1:	 #include <stdio.h>
2:	 
3:	 #define SUCCESS 1
4:	 #define FAILURE 0
5:	 
6:	 #define MAX_WORDS 100000
7:	 #define MAX_LENGTH 1024
8:	 
9:	 
10:	 /* words.c: print some statistics about the words in a 
11:	    file of words with one word per line */
12:	 
13:	 typedef struct word_struct{
14:	   char letters[MAX_LENGTH];
15:	   int length;
16:	 } word;
17:	 
18:	 word* words[MAX_WORDS];
19:	 int num_words = 0;
20:	 
21:	 void show_help(void) {
22:	   printf("Usage: words [-w|-c] filename\n");
23:	   exit(1);
24:	 }
25:	 
26:	 void chomp(char* line) {
27:	   while(*line != 0) {
28:	     if (*line == '\n') {
29:	       *line = 0;
30:	       return;
31:	     }
32:	     line++;
33:	   }
34:	 }
35:	 
36:	 int read_file(char* filename) {
37:	   FILE *file_handle;
38:	   char* char_buf;
39:	   word* cur_word;
40:	 
41:	   file_handle = fopen(filename, "r");
42:	   if (file_handle == NULL) {
43:	     return FAILURE;
44:	   }
45:	 
46:	   char_buf = (char*) malloc(MAX_LENGTH * sizeof(char));
47:	   if (char_buf == NULL) {
48:	     return FAILURE;
49:	   }
50:	 
51:	   do {
52:	     if (!fgets(char_buf, MAX_LENGTH, file_handle)) {
53:	       break;
54:	     }
55:	     chomp(char_buf);
56:	     cur_word = (word*) malloc(sizeof(word));
57:	     if (cur_word == NULL) {
58:	       return FAILURE;
59:	     }
60:	     strncpy(cur_word->letters, char_buf, MAX_LENGTH);
61:	     cur_word->length = strlen(cur_word->letters);
62:	     words[num_words] = cur_word;
63:	     num_words++;
64:	   } while (1);
65:	 
66:	   return SUCCESS;
67:	 }
68:	 
69:	 void count_words() {
70:	   printf("%d\n", num_words);
71:	 }
72:	 
73:	 void count_chars() {
74:	   int i;
75:	   int count = 0;
76:	   for (i=0; i<num_words; i++) {
77:	     count += words[i]->length;
78:	   }
79:	   printf("%d\n", count);
80:	 }
81:	 
82:	 int main (int argc, char* argv[]) {
83:	   if (argc == 3) {  
84:	     if (read_file(argv[2]) == FAILURE) {
85:	       exit(1);
86:	     }
87:	     if (strncmp(argv[1], "-w", 3) == 0) {
88:	       count_words();
89:	       exit(0);
90:	     }
91:	     if (strncmp(argv[1], "-c", 3) == 0) {
92:	       count_chars();
93:	       exit(0);
94:	     }
95:	   }
96:	   show_help();
97:	 }
  1. What .h files are included? Why?
  2. What global variables are in the program?
  3. What does the type word refer to? What fields does it have? How do you access them? What does '->' mean?
  4. Where are the looping constructs? What are the exit conditions?
  5. What functions are defined in the program? What are their signatures? What functions are called by the program? What are their signatures?
  6. What is a library function? Which ones are library functions?
  7. How do we read in command line arguments? What is the value of argc if the program is called like so: 'words -c /usr/dict/words'? What are the contents of argv[0] and argv[1]?
  8. How do we open a file? How do we read data from a file?
  9. Why is there a (char*) or (word*) before the malloc call?
  10. What does chomp do?

Programming Assignment