Practice of Programming

Chapter 1

Exercise 1-1: Comment on the choice of names and values in the following code:

#define TRUE 0
#define FALSE 1

if ((ch = getchar()) == EOF)
  not_eof = FALSE;
  
- Answer:
    - You'd expect TRUE to be 1 and FALSE to be 0.
    - Inconsistent snake case (`getchar` and `not_eof` )

Exercise 1-2: Improve this function

int smaller(char *s, char *t) {
  if (strcmp(s, t) < 1)
    return 1;
  else
    return 0;
}

// improved
#define FALSE 0
#define TRUE 1

int isGreaterLexigraphically(char *s, char *t) {
  if (strcmp(s, t) == 1)
    return TRUE
  else
    return FALSE
}

Exercise 1-4: Improve each of these fragments:

if ( !(c == 'y' || c == 'Y') )
  return;

// Solution:
if ((c != 'y') && (c != 'Y'))
  return;

length = (length < BUFSIZE) ? length : BUFSIZE;

// Solution:
if (length >= BUFSIZE) {
  length = BUFSIZE
}

flag = flag ? 0 : 1;

// Solution:
if (flag)
  flag = 1
else
  flag = 0

quote = (*line == '"') ? 1 : 0;

// Solution
if (*line == '"')
  quote = 1
else
  quote = 0

if (val & 1)
  bit = 1
else
  bit = 0

// Solution
if (val & 1 > 0)
  bit = 1
else
  bit = 0
  
Exercise 1-5: What is wrong with this excerpt?

int read(int *ip) {
  scanf("%d", ip);
  return *ip;
}

insert(&graph[vert], read(&val); read(&ch));

// Which read will take place first? This matters because
// different values will be populated in val and ch
// These two read calls should be placed on separate lines.

Exercise 1-6: List all the different outputs this could produce with various orders of evaluation

n = 1
printf("%d %d\n", n++, n++)

// "1 2"
// "2 1"
// "2 3"
// "3 2"

Exercise 1-7: Rewrite the C excepts more clearly:

if (istty(stdin))    ;
else if (istty(stdout))   ;
     else if (istty(stderr))   ;
           else return(0);

if (retval != SUCCESS)
{
  return (retval);
}
// All went well!
return SUCCESS;

for (k = 0; k++ <5; x += dx)
  scanf("%lf",  &dx);

// Solutions
if (!istty(stdin) && !istty(stdout) && !istty(stderr))    ;
	else return 0;

if (retval == SUCCESS)
  return SUCCESS;
else
  return retval;

for (i = 0; i < 5; , i++) {
  scanf("%lf",  &dx);
  x += dx;
}

Exercise 1-8: Identify the errors in this Java fragment and repair it by rewriting with an idiomatic loop:

int count = 0;
while (count < total) {
  count++;
  if (this.getName(count) == nametable.userName()) {
    return (true);
  }
}

// Solution
for (int count = 0; count < total; count++) {
  if (this.getName(count) == nametable.userName()) {
    return true;
  }
}

Exercise 1-9: Identify the problems with this macro definition:

#define ISDIGIT(c) ((c >= '0') && (c <= '9')) ? 1 : 0 

// Since the parameter c is used twice in the expression,
// side effects could result depending on how this macro
// is called.

Exercise 1-10: How would you rewrite these definitions to minimize potential errors?

define FT2METER 0.3048
define METER2FT 3.28084
define MI2FT    5280.0
define MI2KM    1.609344
define SQMI2SQKM 2.589988

// Solution: Write them in terms of each other when you
// can. ie,
// define METER2FT 1 / FT2METER

Exercise 1-11: Comment on these comments.

void dict::insert(string& w)
// returns 1 if w in dictionary, otherwise returns 0
// => contradicts code which returns nothing

if (n > MAX || n % 2 == 0) // test for an even number
// better if this was placed in a well-named function
  
// Write a message
  // Add to line counter for each line written
  void write_message()
{
  // increment line counter
  line_number = line_number + 1
  fprintf(fout, "%d %s\n%d %s\n%d %s\n"),
    line_number, HEADER,
    line_number+1, BODY,
    line_number+2, TRAILER);
  // increment line counter
  line_number = line_number + 2;
}