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Structured Programming The Basics

Structured Programming The Basics. 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

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Structured Programming The Basics

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  1. Structured ProgrammingThe 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. Body LOOP(repetition) WHILE Condition DO Statement1 False . . . Condition True

  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

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