elsif -- starts an alternate condition within an if-statement

 
if (...) then 
  ... 
elseif (...) 
  ... 
elsif (...) then 
  ... 
else 
  ... 
endif 

The elsif-statement is used to select a single alternative among a seriesof choices. With each elsif-statement you may specify a condition, which is tested, if the main condition (specified with the if-statement) has failed. Note that elsif might be just as well written as elseif.
Within the example below, two variables a and b are tested against a rangeof values. The variable a is tested with the elsif-statement. The very same tests are performed for the variable b too; but here an involved series of if-else-statements is employed, making the tests much more obscure.

 
input "Please enter a number: " a 
if (a<0) then 
	print "less than 0" 
elseif (a<=10) then 
	print "between 0 and 10" 
elsif (a<=20) 
	print "between 11 and 20" 
else 
	print "over 20" 
endif 

input "Please enter another number: " b 
if (b<0) then 
	print "less than 0" 
else 
	if (b<=10) then 
		print "between 0 and 10" 
	else 
		if (b<=20) then 
			print "between 11 and 20" 
		else 
			print "over 20" 
		endif 
	endif 
endif 

  Note, that the very same tests are performed for the variables a and b, but can be stated much more clearly with the elsif-statement.
  Note, that elsif might be written as elseif too, and that the keyword then is optional.