Which is more appropriate way of programmming

Question

If a variable can take n values should we check for the validity of the values or assume that if all the n-i checks fail it would be the nth value.

For example if we have a variable that stores gender as M or F. Use this:

If gender = "M"
   do male_processing
else
   do female_processing
endif

Or this:

If gender = "M"
  do male_processing
else
  if gender = "F"
     do female_processing
  else
     print "Something has gone wrong Gender has a value " Gender
  endif

endif

Answer 1

For that example, I wouldn't use IF at all, I'd either use SWITCH for your second example

switch (gender) 
    case "M":
        do male_processing
        break
    case "F":
        do female_processing
        break
    default:
        print "Something has gone wrong Gender has a value " Gender
 endswitch

or for your first example, I'd simply treat exceptions as an error using ASSERT

assert (gender = "M" or gender = "F")

Answer 2

Shortly - that depends on what type the variable is. If it's a boolean or an enumeration of some sort and there's no other value it can possible have (including null), a simple else clause will suffice.

You can even add a simple comment like so:

if male:
    do_male_stuff()
else: #obviously female
    do_female_stuff()

Having something like this just seems wrong:

bool = SOME_BOOLEAN_VALUE
if bool:
    do1()
elif not bool:
    do2()
else:
    huh() #?!?!

Bottom line: have an if/else/else if clause for each possible scenario, but no more than that, and keep it readable.

Answer 3

...or, in OO world you could create a base class, say Gender and extend it with Male and Female classes. Instead of assigning value 'M' or 'F' to a variable, you could assign an instance of Male or Female class. Then simply call a method specified in the base class, for example doGenderSpecificStuff(). No need for if-elses there.