Range and step · Procedural

Build the idea

Start with the concept and its key vocabulary.

Key idea

Use ERL step and Python range(start, stop, step) to control loop values.

A step changes the loop variable by an amount other than one. Positive steps count upwards and negative steps count downwards. ERL still includes its to value when the step reaches it. Python range(start, stop, step) still excludes stop, even with a negative step.

Step

The amount added to the loop variable after each iteration.

Ascending

Moving from a smaller value to a larger value.

Descending

Moving from a larger value to a smaller value.

Off-by-one error

A logic error caused by starting or stopping one position too early or too late.

Keep these in mind

ERL writes step after the inclusive end value.
Python writes the step as the third range argument.
A descending range needs a negative step.
To include zero in a Python countdown, use a stop below zero.

Build the idea

Start with the concept and its key vocabulary.

Key idea

Use ERL step and Python range(start, stop, step) to control loop values.

Step

The amount added to the loop variable after each iteration.

Ascending

Moving from a smaller value to a larger value.

Descending

Moving from a larger value to a smaller value.

Off-by-one error

A logic error caused by starting or stopping one position too early or too late.

Keep these in mind

ERL writes step after the inclusive end value.
Python writes the step as the third range argument.
A descending range needs a negative step.
To include zero in a Python countdown, use a stop below zero.