knking.com -- Programming Language Books and Training

 C C++ Java

Books by K. N. King

Home
Books by K. N. King
Short courses
Recommended books
Recommended links
FAQ

C Programming: A Modern Approach (Second Edition)

Chapter 13

Answers to Selected Exercises

2. [was #2]

(a) Illegal; p is not a character.
(b) Legal; output is a.
(c) Legal; output is abc.
(d) Illegal; *p is not a pointer.

4. [was #4]

(a)

int read_line(char str[], int n)
{
  int ch, i = 0;

  while ((ch = getchar()) != '\n')
    if (i == 0 && isspace(ch))
      ;   /* ignore */
    else if (i < n)
      str[i++] = ch;
  str[i] = '\0';
  return i;
}

(b)

int read_line(char str[], int n)
{
  int ch, i = 0;

  while (!isspace(ch = getchar()))
    if (i < n)
      str[i++] = ch;
  str[i] = '\0';
  return i;
}

(c)

int read_line(char str[], int n)
{
  int ch, i = 0;

  do {
    ch = getchar();
    if (i < n)
      str[i++] = ch;
  } while (ch != '\n');
  str[i] = '\0';
  return i;
}

(d)

int read_line(char str[], int n)
{
  int ch, i;

  for (i = 0; i < n; i++) {
    ch = getchar();
    if (ch == '\n')
      break;
    str[i] = ch;
  }
  str[i] = '\0';
  return i;
}

6. [was #6] 

void censor(char s[])
{
  int i;

  for (i = 0; s[i] != '\0'; i++)
    if (s[i] == 'f' && s[i+1] == 'o' && s[i+2] =='o')
      s[i] = s[i+1] = s[i+2] = 'x';
}

Note that the short-circuit evaluation of && prevents the if statement from testing characters that follow the null character.

8. [was #10] tired-or-wired?

10. [was #12] The value of q is undefined, so the call of strcpy attempts to copy the string pointed to by p into some unknown area of memory. Exercise 2 in Chapter 17 discusses how to write this function correctly.

15. [was #8]

(a) 3
(b) 0
(c) The length of the longest prefix of the string s that consists entirely of characters from the string t. Or, equivalently, the position of the first character in s that is not also in t.

16. [was #16] 

int count_spaces(const char *s)
{
  int count = 0;

  while (*s)
    if (*s++ == ' ')
      count++;
  return count;
}

Answers to Selected Programming Projects

1. [was #14] 

#include <stdio.h>
#include <string.h>

#define WORD_LEN 20

void read_line(char str[], int n);

int main(void)
{
  char smallest_word[WORD_LEN+1],
       largest_word[WORD_LEN+1],
       current_word[WORD_LEN+1];

  printf("Enter word: ");
  read_line(current_word, WORD_LEN);
  strcpy(smallest_word, strcpy(largest_word, current_word));

  while (strlen(current_word) != 4) {
    printf("Enter word: ");
    read_line(current_word, WORD_LEN);
    if (strcmp(current_word, smallest_word) < 0)
      strcpy(smallest_word, current_word);
    if (strcmp(current_word, largest_word) > 0)
      strcpy(largest_word, current_word);
  }

  printf("\nSmallest word: %s\n", smallest_word);
  printf("Largest word: %s\n", largest_word);

  return 0;
}

void read_line(char str[], int n)
{
  int ch, i = 0;

  while ((ch = getchar()) != '\n')
    if (i < n)
      str[i++] = ch;
  str[i] = '\0';
}

4. [was #18] 

#include <stdio.h>

int main(int argc, char *argv[])
{
  int i;

  for (i = argc - 1; i > 0; i--)
    printf("%s ", argv[i]);
  printf("\n");

  return 0;
}

6. [was #20] 

#include <ctype.h>
#include <stdio.h>
#include <string.h>

#define NUM_PLANETS 9

int string_equal(const char *s, const char *t);

int main(int argc, char *argv[])
{
  char *planets[] = {"Mercury", "Venus", "Earth",
                     "Mars", "Jupiter", "Saturn",
                     "Uranus", "Neptune", "Pluto"};
  int i, j;

  for (i = 1; i < argc; i++) {
    for (j = 0; j < NUM_PLANETS; j++)
      if (string_equal(argv[i], planets[j])) {
        printf("%s is planet %d\n", argv[i], j + 1);
        break;
      }
    if (j == NUM_PLANETS)
      printf("%s is not a planet\n", argv[i]);
  }

  return 0;
}

int string_equal(const char *s, const char *t)
{
  int i;

  for (i = 0; toupper(s[i]) == toupper(t[i]); i++)
    if (s[i] == '\0')
      return 1;

  return 0;
}
Copyright © 2008, 1996 W. W. Norton & Company, Inc. All rights reserved.

Google
 
Web knking.com