Three Programming Control Structures
See also: Programs are Algorithms and Modular Programming

Structure

Note that all programs are primarily
Sequences, - the statements in code are sequential (even when the sequences are run in parallel or concurrently).
More precisely, we can say that the essential characteristic of structured code is 

linearity of control

'Control' is passed from statement to statement sequentially.

Linearity of control requires that all program constructs have:

a single entry point and a single exit point

with only defined legal violations of these requirements (e.g. premature exit from an iteration - loop).


The following diagrams demonstrate the use of
Logic Flowcharts and Structured English to describe programming control structures.

Sequence

Selections - IF and CASE


 
Iterations - Loops


Tony Drewry
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