Effective Programming Style Guidelines

The Elements of Programming Style

References The elements of programming style by Kernighan and Plauger The practice of programming by Kernighan and Pike The pragmatic programmer by Hunt and Thomas

What distinguishes journeyman from master? Attitude Style Philosophy

Documentation The only reliable document is the code. A comment is of <=0 value if it is wrong. Make sure comments and code agree. Don t just echo the code with comments make every comment count. Don t comment on bad code rewrite it. Comment functions and global data. Don t over-comment.

Names Use descriptive names for globals, short names for locals. Be consistent. Use active names for functions. Be accurate.

Using descriptive names for globals and short names for locals. int npending = 0; for (theElementIndex=0; theElementIndex<numberOfElements; theElementIndex++) elementArray[theElementIndex] = theElementIndex; for (i =0; i<nElem; i++) arr[i] = i;

Be consistent. class UserQueue { int noOfItemsInQ, frontOfTheQueue, queueCapacity; . } class UserQueue { int nitems, front, capacity; . }

Use active names for functions int getHour(); bool isEven(int n);

Be accurate bool isOdd(int num) { return (num%2 == 0); }

Expressions and statements Say what you mean, simply and directly. Use the natural form for expression. Parenthesize to resolve ambiguity. Break up complex expressions. Replace repetitive expressions by calls to a common function. Be careful with side effects. Use the telephone test for readability.

Say what you mean, simply and directly. int v[10][10]; for (int i = 1; i<=10; i++) for (int j = 1; j<=10; j++) v[i-1][j-1] = (i/j)*(j/i);

Use natural form for expression if (!(block_id < actblks) || !(block_id >= unblocks)) if ((block_id >= actblks) || (block_id < unblocks))

Parenthesize to resolve ambiguity. *this.hour (*this).hour or *(this.hour)?

Break up complex expression *x += (*xp = (2*k <(n-m)?c[k+1];d[k--])); if (2*k < (n-m)) *xp = c[k+1]; else *xp = d[k--]; *x += *xp;

Be careful with side effects scanf( %d %d , &yr, &profit[yr]); scanf( %d , &yr); scanf( %d , &profit[yr]);

Consistency and idioms Use a consistent indentation and brace style. Use idioms for consistency. Use else-if for multi-way decision.

Use idiom for consistency i = 0; while (i <= n-1) array[i++] = 1.0; for (i=0;i<n;) array[i++] = 1.0; for (i=n;--i>=0;) array[i] = 1.0; for (i=0;i<n;i++) array[i] = 1.0;

Use idiom for consistency do { c = getchar(); putchar(c); } while (c!=EOF); while ((c=getchar())!=EOF) putchar(c);

Use idiom for consistency int i, *iArray, nmemb; iArray = malloc(nmemb*sizeof(int)); for (i = 0; i<=nmemb; i++) iArray[i]=i; int i, *iArray, nmemb; iArray = malloc(nmemb*sizeof(int)); for (i = 0; i<nmemb; i++) iArray[i]=i;

Use else-if for multi-way decisions if (argc == 3) if ((fin=fopen(argv[1], r )) !=NULL) if ((fout = fopen(argv[2], w )) != NULL) { while ((c = getc(fin)) !=EOF) putc(c,fout); fclose(fin); fclose(fout); } else printf( Can t open output file %s\n , argv[2]); else printf( Can t open input file %s\n , argv[1]); else printf( Usage: cp input file output file\n );

Use else-if for multi-way decisions if (argc != 3) printf( Usage: cp input file output file\n ); else if ((fin=fopen(argv[1], r )) ==NULL) printf( Can t open input file %s\n , argv[1]); else if ((fout = fopen(argv[2], w )) == NULL) printf( Can t open output file %s\n , argv[2]); else { while ((c = getc(fin)) !=EOF) putc(c,fout); fclose(fin); fclose(fout); }

Avoid function macros #define isupper(c) ((c)>= A && (c) <= Z ) while (isupper(a = getchar())) #define isupper(c) ((c)>= A && (c) <= Z ) while ((a=getchar() !=EOF) && isupper(a))

Parenthesize the macro body and arguments #define square(x) (x)+(x) 1/square(y) will be expanded to 1/(y)+(y) #define square(x) ((x)*(x)) 1/square(y) will be expanded to 1/((y)+(y))