Chapter 2 Problem Solving Techniques

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Chapter 2Problem Solving Techniques
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• 2.1 INTRODUCTION
• 2.2 PROBLEM SOLVING
• 2.3 USING COMPUTERS IN PROBLEM SOLVING THE
  SOFTWARE DEVELOPMENT METHOD

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• consists of the following steps
• 1. Requirements specification
• 2. Analysis
• 3. Design
• 4. Implementation
• 5. Testing and verification
• 6. Documentation
• divide and conquer split the problem into
  several simpler subproblems, solve each
  individually, and then combine these solutions.

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• 2.4 REQUIREMENTS SPECIFICATION
• understanding exactly what the problem is, what
  is needed to solve it, what the solution should
  provide.
• 2.5 ANALYSIS
• identify the following
• 1. Inputs to the problem
• 2. Outputs expected from the solution
• 3. Any special constraints or conditions
• 4. Formulas or equations to be used

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• 2.6 DESIGN AND REPRESENTATION OF ALGORITHMS
• An algorithm is a sequence of a finite number of
  steps arranged in a specific logical order,
  which, when executed, produce the solution for a
  problem.
• An algorithm is a procedure that takes a set of
  values as input and transforms them into a set of
  values as output
• In practice we expect algorithms to be efficient.

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• Pseudocoding
• The main purpose of a pseudocode language is to
  define the procedural logic of an algorithm
• requirements
• 1. Have a limited vocabulary
• 2. Be easy to learn
• 3. Produce simple, English-link narrative
  notation
• 4. Be capable of describing all algorithms

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• The Sequence Control Structure
• is a series of steps or statements that are
  executed in the order in which they are written
  in an algorithm
• read taxable income
• read filing status
• compute income tax
• print income tax
• Figure 2.1 A sequence control structure

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• The Selection Control Structure
• define two courses of action, depending on the
  outcome of a condition.
• if condition
• then-part
• else
• else-part
• end_if
• the else-part may be missing.

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• A nested selection structure contains other
  if/else structures in its then-part or else-part.
• if status is equal to 1
• print single
• else if status is equal to 2
• print Married filing jointly
• end_if

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• if status is equal to 1
• print Single
• end_if
• if status is equal to 2
• print Married filing jointly
• end_if

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• The Repetition Control Structure
• specifies a block of one of one or more
  statements that are repeatedly executed until a
  condition is satisfied.
• while condition
• loop-body
• end_while
• loop-body is a single statement or a block of
  statements

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• Print Enter taxable income should be greater
  than or equal to 50,000.00 read income
• while income is less than 50000.00
• begin
• print Enter taxable income should be
  greater than or equal to 50,000.00
• read income
• end
• end_while

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• Conventions for Pseudocoding
• Each pseudocode statement includes keywords
• Each pseudocode statement should be written on a
  separate line.
• Statements in a sequence structure can be grouped
  into a block
• For the selection control structure, use an
  if/else statement.
• For the repetition control structure, use the
  while statement
• All words in a pseudocode statement must be
  unambiguous and as easy as possible for
  nonprogrammers to understand.

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• Structure chart, as in figure 2.6. This chart
  indicates that the original problem is solved if
  the four subproblems at the lover level of
  hierarchy are solved from left to right.

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• set correctStatusInput to no
• print FILING STATUS MENU
• print Single ----1
• print Married filing jointly ----2
• print Married filing separately ----3
• print Head of household ----4
• while correctStatusInput is equal to no
• begin
• print Enter filing status should be between
  1 and 4
• read filingStatus
• if filingStatus is greater than 0
• if filingStatus is less than 5
• set correctstatusInput to yes
• end_if
• end_if
• end
• end_while
• Figure 2.7 Final refinement of read and verify
  filing status

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• if filingStatus is 1
• compute tam 11158.50 0.31 (income
  49300.00)
• else if filingStatus is 2
• if income is less than or equal to 82,150
• compute tax 5100.00 0.28 (income
  34000.00)
• else
• compute tax 18582.00 0.31 (income
  82150.00)
• end_if
• else if filingStatus is 3
• compute tax 9291.00 0.31 (income
  41075.00)
• else if status is 4
• if income is less than or equal to 70450.00
• compute tax 4095.00 0.28 (income
  27300.00)
• else
• compute tax 16177.00 0.31 (income
  70450.00)
• end_if
• end_if
• Figure 2.8 Final refinement of compute tax
  (continued)

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• print income
• if filingStatus is equal to 1
• print Single
• else if filingStatus is equal to 2
• print Married filing jointly
• else if filingStatus is equal to 3
• print married filing separately
• else if filingStatus is equal to 4
• print Head of household
• end_if
• print tax
• Figure 2.9 Final refinement of print income,
  filing status, and tax

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• Algorithm design technique
• Use the divide-and-conquer strategy to split the
  original problem into a series of subproblems.
• Consider each subproblem separately and further
  split them into subproblems, until no further
  refinement is possible. Stop the process when you
  have a pseudocode that can be directly translated
  into a C program.
• Combine all final refinements

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• Flowcharting
• alternative to pseudocoding
• flowchart is a graph consisting of geometrical
  shapes
• the geometrical shapes in a flowchart represent
  the types of statements in an algorithm. The
  details of statements are written inside the
  shapes. The flow lines show the order in which
  the statements of an algorithm are executed. Two
  geometrical shapes used in flowcharting are the
  rectangle, which represents processes such as
  computations, assignments, and initializations,
  and the diamond-shaped box, which stands for the
  keyword if in pseudocode, with the if condition
  written inside the box.

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• 2.7 IMPLEMENTATION
• translate each step of the algorithm into a
  statement in that particular language
• Programming Errors
• debugging
• three types of programming errors
• 1. design errors occur during the
  analysis,design, and implementation phases.
• 2. Syntax error detected by the compiler
  during the compilation process.
• 3. Run-time errors detected by the computer
  while your program is being executed. Divide a
  number by zero.

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• 2.8 TESTING AND VERIFICATION
• A program must be tested using a sufficiently
  large sample of care fully designed test data
  sets such that every logical path in the program
  is traversed at least once.

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• 2.9 PROGRAM DOCUMENTATION
• 1. A concise requirements specification
• 2. Descriptions of problem inputs, expected
  outputs, constraints, and applicable formula.
• 3. A pseudocode or flowchart for its algorithm
• 4. A source program listing
• 5. A hard copy of a sample test run of the
  program
• 6. A users guide explaining to nonprogrammer
  users how the program should be used (optional)