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COMP2004
Programming Practice
2002 Summer School


Kevin Pulo
School of Information Technologies
University of Sydney

Using &

• & has 2 different meanings depending on where it's used

• In front of an object
  • Takes the address
  • int* p = &i;

• In a function parameter definition
  • Pass by reference
  • int sum(std::vector &v)

Code style

• Indenting
• Whitespace
• Identifiers
• Structure
• Comments
• Bracketing

• In all cases aim to make your code
  • Easily readable
  • Consistent

Indenting

• By far the most important
• Choose a certain number of spaces and stick with it
• Common ones are 8, 4 and 2
• Indent code inside control structures
  • functions, if(), while(), for(), etc

Bad Indenting 1

double a_function(int a) {
int b = 0;
double c;
while(b < 100) {
if (a == b) {
c = 34.2; }
else
{ c = 12.8;
}
}
}

Bad Indenting 2

double a_function(int a) {
int b = 0;
double c;
while(b < 100) {
if (a == b) {
c = 34.2; }
else
{c = 12.8;
}
}
}

Good Indenting

double a_function(int a) {
int b = 0;
double c;
while(b < 100) {
if (a == b) {
c = 34.2;
} else {
c = 12.8;
}
}
}

Whitespace

• Groups related code together
• Vertical
  • Blank lines between functions, code paragraphs
• Horizontal
  • Spaces around operators, brackets, etc

Bad Vertical Whitespace

unsigned int numDigits(unsigned long x) {
return static_cast(log10(x)) + 1;
}
void getDigits(std::vector &digits, unsigned long number) {
unsigned int i, n;
n = numDigits(number);
digits.resize(n);
for (i = n - 1; i > 0; i--) {
digits[i] = number % 10;
number = number / 10;



}
digits[i] = number;
}
int main() {
unsigned int number;
while (std::cin >> number) {
std::vector digits;
getDigits(digits, number);
std::cout << digits[0];
for (int i = 1; i < digits.size(); i++)
std::cout << ", " << digits[i];
std::cout << std::endl;
}
}

Good Vertical Whitespace

unsigned int numDigits(unsigned long x) {
return static_cast(log10(x)) + 1;
}


void getDigits(std::vector &digits, unsigned long number) {
unsigned int i, n;

n = numDigits(number);
digits.resize(n);
for (i = n - 1; i > 0; i--) {
digits[i] = number % 10;
number = number / 10;
}
digits[i] = number;
}


int main() {
unsigned int number;

while (std::cin >> number) {
std::vector digits;
getDigits(digits, number);

std::cout << digits[0];
for (int i = 1; i < digits.size(); i++)
std::cout << ", " << digits[i];
std::cout << std::endl;
}
}

Horizontal Whitespace

• if((d>=1)&&(d<=maxDays))

• if ((d >= 1) && (d <= maxDays))

• for(i=s.size()-1;i>0;--i)

• for (i=s.size()-1; i>0; --i)

• for ( i = s.size() - 1 ; i > 0 ; --i )

Identifiers

• Names of variables, functions, enums, etc
• Descriptive and concise
• Nouns for variables, verbs for functions
• Singular for variables, plurals for collections
• Consistent scheme for multiple-word identifiers
  multipleWordIdentifiermultiple_word_identifier

Bad Identifiers

• Anything one letter long (except i as a loop iterator)
  • eg: a, b, c, d, ...
• Identifiers which vary by only 1 character
  • eg: item0, item1, item2, ...
• If these items are related, consider an array/vector instead
  • eg: item[0], item[1], item[2], ...

Bad Identifiers

• Unnecessary abbreviations and spelling mistakes
  • eg: nmItms, piont
  • better: numItems, point
• Unnecessarily long/verbose
  • eg: number_of_elements_in_array
  • better: num_elems

Structure

• High cohesion
  • Each function performs exactly one task
• Low coupling
  • Each function has minimal reliance on other functions
• Low cohesion and high coupling make code hard to read and maintain
• eg. solution for Week 1 Wed Q4

Comments

• Describe the code's purpose / meaning
• Don't just restate the code in English

• i++; // Increment i
  • Bad
• i++; // Make i be 1 bigger
  • Still bad
• i++; // Move to next vector element
  • Better

Comments

• Each of these should have a comment
  • Entire program
  • Every function (except main())
    • Mention parameters and return value
  • Every large code paragraph
  • Every important variable
  • Complex or hard-to-understand statements and expressions

Comment syntax


int i; // Comment to end-of-line
int i; /* Comment with begin and end */

int i;
#if 0
Large block comment
#endif

Comment syntax

• //
  • Best for small comments

• /* */
  • Can appear anywhere
  • Not nestable

if ((d >= 1) && (d /*<=*/ maxDays)) if ((d >= 1) /* && (d /*<=*/ maxDays)*/) if ((d >= 1) maxDays)*/)

Comment syntax

• #if 0
• #endif
  • Must appear on own line
  • Nestable
  • Most useful for removing large sections of code while debugging/ testing

Bracketing

• Several styles - just be consistent

if (a == b) do_something();

if (b == c)
{
part_1();
part_2();
}
else
something_else();

Another bracketing style

if (a == b) {
do_something();
}

if (b == c) {
part_1();
part_2();
} else {
something_else();
}

Simple g++ errors

• Line number usually most useful

1: #include
2: int main() {
3: int i = 42;
4: int* p = *i;
5: cout << &p << endl;
6: }
bash$ g++ -Wall -g -o prog prog.ccprog.cc: In function `int main()':
prog.cc:4: invalid type argument of `unary *'



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