Programming Style

1
Programming Style

• CSE 105
• Structured Programming Language
• Presentation - 2

Thanks to Arie Rapoport, cs.huji.ac.il
2
Word Counting (KnR 1.5.4)
Start
stateOUT nlnwnc0

• include ltstdio.hgt
• define IN 1 / inside a word /
• define OUT 0 / outside a word /
• / count lines, words, and characters in input /
• main( )
• int c, nl, nw, nc, state
• state OUT
• nl nw nc 0
• while ((c getchar()) ! EOF)
• nc
• if (c \n)
• nl
• if (c c \n c \t)
• sate OUT

c getchar()
c ! EOF
N
Y
nc
c\n
N
Y
nl
c is white- char
state OUT
N
Y
Y
state OUT
stateIN nw
print nl,nw,nc
End
3
Program Style

• Readability
• Clarity
• Common sense
• Right focus

4
Whats in a name

• Example
• define ONE 1
• define TEN 10
• define TWENTY 20
• More reasonable
• define INPUT_MODE 1
• define INPUT_BUFSIZE 10
• define OUTPUT_BUFSIZE 20

5
Whats in a name

• Use descriptive names for global variables
• int npending 0 // current length of input
  queue
• Naming conventions vary
• numPending
• num_pending
• NumberOfPendingEvents

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Whats in a name

• Compare
• for( theElementIndex 0
• theElementIndex lt numberOfElements
• theElementIndex )
• elementArraytheElementIndex
  theElementIndex
• and
• for( i 0 i lt nelems i )
• elemi i
• Use short names for locals

7
Whats in a name

• Consider
• int noOfItemsInQ
• int frontOfTheQueue
• int queueCapacity
• The word queue appears in 3 different ways
• Be Consistent
• Follow naming guidelines used by your peers

8
Whats in a name

• Use active name for functions
• now getDate()
• Compare
• if( checkdigit(c) )
• to
• if( isdigit(c) )
• Accurate active names makes bugs apparent

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Indentation

• Use indentation to show structure
• Compare
• for(n n lt100 fieldn 0)
• c 0 return \n
• to
• for( n n lt100 n)
• fieldn 0
• c 0
• return \n

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Expressions

• Use parenthesis to resolve ambiguity
• Compare
• leap_year y 4 0 y 100 ! 0
• y 400 0
• to
• leap_year ((y 4 0) (y 100 ! 0))
• (y 400 0)

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Statements

• Use braces to resolve ambiguity
• Compare
• if( i lt 100 )
• x i
• i
• to
• if( i lt 100 )
• x i
• i

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Idioms

• Do not try to make code interesting
• i 0
• while( i lt n 1 )
• arrayi 1
• for( i 0 i lt n )
• arrayi 1
• for( i n --i gt 0 )
• arrayi 1
• for( i 0 i lt n i )
• arrayi 1

This is the common idiom that any programmer
will recognize
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Idioms

• Use else if for multi-way decisions
• if ( cond1 )
• statement1
• else if ( cond2 )
• statement2
• else if ( condn )
• statementn
• else
• default-statement

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Idioms

• if( x gt 0 )
• if( y gt 0 )
• if( xy lt 100 )
• ...
• else
• printf(Too large!\n" )
• else
• printf("y too small!\n")
• else
• printf("x too small!\n")

• if( x lt 0 )
• printf("x too small!\n")
• else if( y lt 0 )
• printf("y too small!\n")
• else if( xy gt 100 )
• printf("Sum too large!\n" )
• else
• ...

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Comments

• Dont belabor the obvious
• // return SUCCESS
• return SUCCESS
• // Initialize total to number_received
• total number_received
• Test does comment add something that is not
  evident from the code

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Comments

• Document each function
• // random return a random integer in 0..r
• int random( int r )
• return (int)floor(rand()r)

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Comments

• A more elaborate function comment
• //
• // GammaGreaterThanOne( Alpha )
• //
• // Generate a gamma random variable when alpha gt
  1.
• //
• // Assumption Alpha gt 1
• //
• // Reference Ripley, Stochastic Simulation, p.90
  
• // Chang and Feast, Appl.Stat. (28) p.290
• //
• double GammaGreaterThanOne( double Alpha )

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Comments

• Dont comment bad code rewrite it!
• // If result 0 a match was found so return
• // true otherwise return false
• return !result
• Instead
• return matchfound

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Style recap

• Descriptive names
• Clarity in expressions
• Straightforward flow
• Readability of code comments
• Consistent conventions idioms

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Why Bother?

• Good style
• Easy to understand code
• Smaller polished
• Makes errors apparent
• Yields a good grade
• Sloppy code ?bad code
• Hard to read
• Broken flow
• Harder to find errors correct them, maintenance.