1. Structured Programming The Basics

2. Structured Programming
Early programmers had to learn to program ad hoc – try things and see if they worked
Early software engineers studied software projects to see why some succeeded and some failed
They found patterns of programming that usually give good results when followed
These are the rules of structured programming

3. Control Structures and Data Structures
Control structures and data structures are the main components of any program
Data structures allow you to access your data
Simplest is a literal constant like 5
Variables are simple data structures – have a name, a value, a type, a location (address) in RAM
Lists, files, graphics objects are more complex data structures

4. Control structures They control the order of execution
What order statements will be done in, or whether they will be done at all (whether they are skipped or not)
Different from data structures

5. Why do structured programming?
It's easier to understand code written using structured programming
Easier to test and debug code
Easier to modify and maintain code
Easier to work with other people to write large programs

6. 4 Control Structures
Sequence
Selection
Iteration
Module

7. Guarantees for All Structures
ONE Entrance
ONE Exit

8. SEQUENCE
Statement 1
Statement 2
Statement 3
. . .

9. Guarantees for Sequences
Will execute the steps in the order given
Will not enter or leave sequence in mid-stream
Will not skip steps

10. SELECTION(branch) IF Condition THEN Statement1 ELSE Statement2 True
Statements1
Statement
Condition
. . .
Statements2
False

11. Selection Guarantees
Control always enters through the condition / question
One branch or the other is executed, never both on one run
MUST execute one branch or the other
Processes in branches can be as large or small as you want
Do not write Dead Code!

12. Dead Code

13. LOOP(repetition) WHILE Condition DO Statement1 False . . . Condition
True
Body

14. Guarantees Will go through test / condition at top to get into loop
ALL of body will be executed before test is done again
Body will be repeated until test is answered differently (NO)
Do not write Infinite Loops! (usually a logic error in the controlling condition at the top)

15. SUBPROGRAM(function)
. . .
SUBPROGRAM1
SUBPROGRAM1
a meaningful collection
of SEQUENCES,
SELECTIONS, LOOPS,
SUBPROGRAM calls

16. Module Flow of control