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Sorting Algorithms Coding Style

For student it is important to understand the flowchart and C-implementation. After that you can "objectify", javafy" or "Cpp-fy" or distort in other inventive ways the basic algorithm at your own pleasure ;-) The key ideas are simpler to understand in flowcharts and C or assembler.

General style of C implementations of sorting algorithms is essentially traditional C programming style. Common convertions include

 Only one statement should occur per line

For example, in Java this would involve having statements written like this:

++a;
b = a;

But not like this:

++a; b = a;

Boolean values in decision structures

Some programmers suggest that coding where the result of a decision is merely the computation of a Boolean value, are overly verbose and error prone. They prefer to have the decision in the computation itself, like this:

return (hours < 24) && (minutes < 60) && (seconds < 60);

The difference is entirely stylistic, because optimizing compilers may produce identical object code for both forms. However, stylistically, programmers disagree which form is easier to read and maintain.

Arguments in favor of the longer form include: it is then possible to set a per-line breakpoint on one branch of the decision; further lines of code could be added to one branch without refactoring the return line, which would increase the chances of bugs being introduced; the longer form would always permit a debugger to step to a line where the variables involved are still in scope.

Left-hand comparisons

In languages which use one symbol (typically a single equals sign, (=)) for assignment and another (typically two equals signs, (==) for comparison (e.g. C/C++, Java, ActionScript 3, PHP, Perl numeric context, and most languages in the last 15 years), and where assignments may be made within control structures, there is an advantage to adopting the left-hand comparison style: to place constants or expressions to the left in any comparison. [10] [11]


Here are both left and right-hand comparison styles, applied to a line of Perl code. In both cases, this compares the value in the variable $a against 42, and if it matches, executes the code in the subsequent block.

if ($a == 42) { ... }  # A right-hand comparison checking if $a equals 42.
if (42 == $a) { ... }  # Recast, using the left-hand comparison style.

The difference occurs when a developer accidentally types = instead of ==:

if ($a = 42) { ... }  # Inadvertent assignment which is often hard to debug
if (42 = $a) { ... }  # Compile time error indicates source of problem

The first (right-hand) line now contains a potentially subtle flaw: rather than the previous behaviour, it now sets the value of $a to be 42, and then always runs the code in the following block. As this is syntactically legitimate, the error may go unnoticed by the programmer, and the software may ship with a bug.

The second (left-hand) line contains a semantic error, as numeric values cannot be assigned to. This will result in a diagnostic message being generated when the code is compiled, so the error cannot go unnoticed by the programmer.

Some languages have built-in protections against inadvertent assignment. Java and C#, for example, do not support automatic conversion to boolean for just this reason.

The risk can also be mitigated by use of static code analysis tools that can detect this issue.

Looping and control structures

The use of logical control structures for looping adds to good programming style as well. It helps someone reading code to better understand the program's sequence of execution (in imperative programming languages). For example, in pseudocode:

i = 0
 
while i < 5
  print i * 2
  i = i + 1
end while
 
print "Ended loop"

The above snippet obeys the naming and indentation style guidelines, but the following use of the "for" construct may be considered easier to read:

for i = 0, i < 5, i=i+1
  print i * 2
 
print "Ended loop"

In many languages, the often used "for each element in a range" pattern can be shortened to:

for i = 0 to 5
  print i * 2
 
print "Ended loop"

In programming languages that allow curly brackets, it has become common for style documents to require that even where optional, curly brackets be used with all control flow constructs.

for (i = 0 to 5) {
  print i * 2;
}
 
print "Ended loop";

This prevents program-flow bugs which can be time-consuming to track down, such as where a terminating semicolon is introduced at the end of the construct (a common typo):

 for (i = 0; i < 5; ++i);
    printf("%d\n", i*2);    /* The incorrect indentation hides the fact 
                               that this line is not part of the loop body. */
 
 printf("Ended loop");

...or where another line is added before the first:

 for (i = 0; i < 5; ++i)
    fprintf(logfile, "loop reached %d\n", i);
    printf("%d\n", i*2);    /* The incorrect indentation hides the fact 
                               that this line is not part of the loop body. */
 
 printf("Ended loop");

Lists

Where items in a list are placed on separate lines, it is sometimes considered good practice to add the item-separator after the final item, as well as between each item, at least in those languages where doing so is supported by the syntax (e.g., C, Java)

const char *array[] = {
    "item1",
    "item2",
    "item3",  /* still has the comma after it */
};

This prevents syntax errors or subtle string-concatenation bugs when the list items are re-ordered or more items are added to the end, without the programmer's noticing the "missing" separator on the line which was previously last in the list. However, this technique can result in a syntax error (or misleading semantics) in some languages. Even for languages that do support trailing commas, not all list-like syntactical constructs in those languages may support it.

There are some useful variables naming conventions that are widely used in sorting algorithms:


Etc

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