Control Flow as Structured Code Annotations — 2. Dynamic Behavior

Conceptual Advantage

Mapping

PL	NM
...	(all aspects from 1-Static Structure)
instruction execution	add current step number to arrow leading in, then execute by adding to or looking up information in memory table, expression evaluator, or output areas
expression evaluation	copy expression, substitute values, and evaluate it in expression evaluation area
variable declaration	find first blank column in memory table and add name of variable in first row; value added underneath if initialised
variable assignment	find variable in the memory table, strike through existing entry, and add entry to row below.
conditionals and loops	evaluate control expression to 'True' or 'False', then follow relevant labelled control path to next instruction

Draws Attention To

Dynamic view of control flow (actual execution); evaluation of expressions; declaration, initialisation, access and assignment of variables.

Use When

Developing understanding of how basic programming constructs work.

Cost

Code needs carefully selected and formatted to enable annotation.

Details

Created by Peter Donaldson and Quintin Cutts / PLAN C project.

Two stages to TRACS trace

First, mark code with control flow paths and parts of the code containing expressions. Second, start at the top of the program and execute each line adding or looking up any necessary information from the memory table, expression evaluation or output areas.