Structured%20Programming

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Structured Programming

• structured programming A technique for
  organizing and coding computer programs in which
  a hierarchy of modules is used, each having a
  single entry and a single exit point, and in
  which control is passed downward through the
  structure without unconditional branches to
  higher levels of the structure. Three types of
  control flow are used sequential, test, and
  iteration.

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Advantages of Structured Programming

• Easy to writeModular design increases the
  programmer's productivity by allowing them to
  look at the big picture first and focus on
  details later.Several Programmers can work on a
  single, large program, each working on a
  different moduleStudies show structured
  programs take less time to write than standard
  programs.Procedures written for one program can
  be reused in other programs requiring the same
  task. A procedure that can be used in many
  programs is said to be reusable

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• Easy to debugSince each procedure is specialized
  to perform just one task, a procedure can be
  checked individually. Older unstructured programs
  consist of a sequence of instructions that are
  not grouped for specific tasks. The logic of such
  programs is cluttered with details and therefore
  difficult to follow.Easy to UnderstandThe
  relationship between the procedures shows the
  modular design of the program.Meaningful
  procedure names and clear documentation identify
  the task performed by each moduleMeaningful
  variable names help the programmer identify the
  purpose of each variable.Easy to ChangeSince a
  correctly written structured program is
  self-documenting, it can be easily understood by
  another programmer.

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Top Down Design

• Top Down Design is a method of designing
  something that starts with the complete item then
  breaks it down into smaller and smaller
  components. In programming it means breaking a
  difficult task down (divide and conquer) and
  solving pieces independently until every step can
  easily be implemented (successive refinement).

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Dog House Example

• 1. Floor or Base
• 2. Walls
• 2.1 Back Wall
• 2.1.1 Top section2.1.2 Lower section
• 2.2. Left Wall2.3 Right Wall2.4 Front Wall
• 2.4.1 Top section2.4.2 Door section
• 3. Roof
• 3.1 Left Side3.2 Right Side

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• Prepare all sections as described below then join
  sections using nails and glue as specified.
• 1. Floor or Base - cut to specified size and
  smooth edges
• 2. Walls
• 2.1 Back Wall
• 2.1.1 Top section - cut triangular shape2.1.2
  Lower section - cut square shape and glue and
  staple to upper part of wall
• 2.2. Left Wall - cut to specified dimensions2.3
  Right Wall - cut to specified dimensions2.4
  Front Wall
• 2.4.1 Top section - cut triangular piece to
  specified dimensions2.4.2 Door section - use
  jigsaw to cut U shape for the door in square
  shape, staple and glue to top section
• 3. Roof
• 3.1 Left Side - cut to specified dimensions3.2
  Right Side - cut to specified dimensions

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• Hierarchical systems seem to have a property that
  something considered as an undivided entity on
  one level is considered as a composite object on
  the next lowest level of greater detail as a
  result, the natural grain of space or time that
  is applicable at each level decreases by an order
  of magnitude when we shift our attention from one
  level to the next lower one. We understand walls
  in terms of bricks, bricks in terms of crystals,
  crystals in terms of molecules, etc.-----E.
  Dijkstra

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• The Fundamental Principle of Structured
  Programming is that at all times and under all
  circumstances, the programmer must keep the
  program within his intellectual grasp. The
  well-known methods for achieving this can be
  briefly summarized as follows 1) top-down design
  and construction, 2) limited control structures,
  and 3) limited scope of data structures.-----Tom
  Harbron
• A study of program structure has revealed that
  programs can differ tremendously in their
  intellectual manageability. A number of rules
  have been discovered, violations of which will
  either seriously impair or totally destroy the
  intellectual manageability of the program....I
  now suggest that we confine ourselves to the
  design and implementation of intellectually
  manageable programs.-----E. Dijkstra