if ... then ... end if

Conditionally execute code.

Syntax:
if condition expression then
        commands to be executed if condition is true
end if

The if statement allow the execution of certain operations only if determinate conditions are true, this allow your program to make decisions.
To make decision the if statement evaluate the condition expression that is any expression that results in either true or false , for example: 5>1=true or 10<3=false
If the expression is true the commands between statement then and statement end if will be executed otherwise, if the expression is false, it will be skipped.

Example:
for n = 1 to 20
    a=rnd(10)
    print a
    if a>5 then
        print "random number is greater than five"
    end if
next

See also else, elseif, and, or, not and xor commands.