Like all programming languages, PIC Forth has conditional execution and looping. Consider this code:

This gets the value in variable x (x @) compares it to 5 and if the result is true, turns the led pin high. Otherwise, it turns the led low. Note the odd use of then. In Forth, then ends an if block, which is not intuitive if you've used any other programming language. Some versions of Forth let you replace then with endif and you could certainly write that definition using some Forth trickery. But you might as well get used to seeing it this way so when you read other Forth programs you won't be confused.

Of course, the else is optional and you can put as much code as you like in each part of the if statement.

PIC Forth supports looping words like:

begin, again, while, until, and repeat.

Loops generally start with begin and end with repeat, again, while, or until.  So:

begin work 1 counter @ + dup ! $10 > until

This calls the work word and then increments the counter (but leaves a copy of the incremented counter on the stack. Next, it compares the new counter with 10 (hex) and if it is less than or equal to 10, the until word will go back to the top of the loop. Look at the generated code (this requires libstore.fs to be included):

The while word can occur inside the loop to exit the loop early if desired.

Here is a shortcut loop that starts with counter=$10 and works down to zero

PIC Forth optimizes loops pretty well. It even detects tail end recursion and converts it to a goto. You can also add assembly language to your programs...