else -- mark an alternative within an if-statement
if (...) then
The else-statement introduces the alternate branch of an if-statement. I.e. it starts the sequence of statements, which is executed, if the condition of the if-statement is not true.
input "Please enter a number: " a
if (mod(a,2)=1) then
print a," is odd."
print a," is even."
This program detects, if the number you have entered is even or odd.