University of Washington Computer Programming I Program Style 2000 UW CSE M 1 Aspects of Quality Software Getting the syntax right This may seem hard at first but turns out to be the easiest part of all Getting the logic right Sometimes difficult but absolutely essential Today s focus Programming with good style What does this mean and why does it matter M 2 Programming Style A program is a document Some of it is read by a computer ALL of it is read by people Donald Knuth literate programming Style is a catch all term for people oriented programming comments spacing indentation names clear straightforward well organized code code quality M 3 Style in This Course Along the way we suggest and sometimes require particular points of style in programs that are turned in for the on campus version of this course It is common for employers to have style requirements that all programmers must follow M 5 Comments Comment block at front of program Comment block per major section Small ones throughout Program Mi To Km Purpose Miles to Km conversion Author A Hacker 1 18 00 Sec AF Turing Calculate volume of cylinder and Inputs radius height Output volume Assumes radius height nonnegative Tell user it s negative M 6 Required Comments 1 1 Heading comment at the beginning of each file Brief explanation of what s in the file 2 Function heading comments Describe what the function does Must explain define all parameters and result Should never have to read function body to understand how to call it M 7 Required Comments 2 3 Variable declaration comments Describe information contained in the variable Not needed for trivial variables if their usage is obvious loop indices etc Should never have to read code that uses a variable to figure out what s in it 4 Statement comments Higher level summary of what the following group of statements does as needed Say what not how Most individual statements won t need comments M 8 Statement Comments Say why don t paraphrase the code NO subtract one from sheep sheep sheep 1 YES account for the sheep that the big bad wolf just ate sheep sheep 1 M 9 Spaces Use blank lines to separate major sections Vertically align like things x 5 y prime 7 z axis 4 3 Leave space around operators No y slope x intercept Yes y slope x intercept Use parentheses for emphasis too Yes y slope x intercept Indentation Like an outline indent subordinate parts M 10 Identifiers Review Identifiers name variables and other things Letters digits and underscores Can t begin with a digit Not a reserved word like double return Case sensitive VAR Var var vAr are all different Using all CAPITAL letters is legal but usually reserved for define constants soon to be explained M 11 What s in a Name Extremely valuable documentation Microsoft Excel has over 65 000 variables How long is just right m mph miles per hour average miles per hour that the red car went Avoid similar names mph vs Mph vs mqh M 12 Suggestions for Names Variables and value returning functions Noun phrase describing information in variable or value returned by function Void functions Verb phrase describing action performed when function is called M 13 More Examples OK rectangleWidth rectangle Width rectangle width length 10 Rectangle Illegal 10TimesLength My Variable int Legal but bad style a1 I O xggh0sxx89s rectangleWidth and rectanglewidth or rectangle width M 14 Clarity Do obvious things the obvious way No x y x 1 Yes y x x x 1 Don t be tricky cute or clever without GOOD reason If so comment it M 15 define Symbolic Constants review Named constants define PI 3 14159265 define HEIGHT 50 define WIDTH 80 define AREA HEIGHT WIDTH circle area PI radius radius volume length AREA Note and are not used for define can be used in define M 16 Why define review Centralize changes No magic numbers unexplained constants use good names instead Avoid typing errors Avoid accidental assignments to constants double pi pi 3 14 pi 17 2 vs define PI 3 14 PI 17 2 syntax error M 17 Many small points Big cumulative effect include stdio h int main void double v1 v2 v3 v4 v5 printf Enter a number of miles per hour scanf lf v1 v5 v1 14 6666667 printf f miles per hour is equal to v1 printf feet per second n v1 v5 return 0 M 19 Style Summary Clarity is Job 1 DO Use plenty of comments but not too many Use white space Use indentation Choose descriptive names Use named constants DON T be terse tricky place speed above correctness simplicity M 20 use magic numbers
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