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 this type of construct, I like to use the switch statement. Not because it is shorter (it is not), but it is more readable (IMHO):

switch(gender) {
  case "M":
    doMaleSpecificStuff();
    break;
  case "F":
    doFemaleSpecificStuff();
    break;
  default:
    throw AnyError;
}