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```More Algorithm Design
CSIS 1595: Fundamentals of
Programming and Problem Solving 1
Example
• Requirements:
Write program to compute income taxes from gross
income and dependents.
– Tax is a tax rate (currently 20%) of deductible
income.
– Deductible income is gross income minus
deductions.
– Deductions include a standard deduction
(currently \$10,000) and a \$3000 dependent
deduction rate for each dependent.
• What information do you need to keep track of?
– Look for nouns in requirements
– These will often become your variables
• Where will that information come from?
– Input by user?
– Computed from something else?
• If so, how?
Variables in Example
tax
tax_rate
deductible_income
gross_income
deductions
deductible income × tax rate
Set at 20%
gross income minus deductions
Input by user
standard deduction + dependents ×
dependent deduction rate
standard_deduction Set at 10000
dependents
Input by user
dependent_deduction Set at 3000
• Order of steps often determined by data dependency
• Cannot compute variable until values it depends on
is known
– Assign variables with set values
– Prompt user for variables they must provide
– Compute remaining variables in order of
dependencies
Dependencies in Example
• Set tax_rate, standard_deduction, and
dependent_deduction_rate values
• Prompt user for gross_income and dependents values
• Compute deductions from standard_deduction,
dependents, and dependent_deduction
• Compute taxable_income from gross_income and
deductions
• Compute tax from taxable_income and tax_rate
Example Pseudocode
Constants
• Many values considered “named constants”
– Do not change value during program
– May change value in future versions of program
(so should be easy to change in future)
• Define named constant at beginning of code
– Convention: Use all caps to distinguish from variables
TAX_RATE = 0.2
– Use named constant in program instead of value
tax = taxable_income * TAX_RATE
Scaffold Testing
• Problem:
Only output we have for testing is final tax value
• If not correct, error could come from any (or several)
previous calculations
– Computation of deductions
– Computation of taxable income
– Computation of tax
Scaffold Testing
• Solution:
Print all intermediate values as they are computed
– deduction
– taxable_income
• Make sure these computed in advance for test
• Can comment out when finished
– Do not delete, since may need in future!
Scaffold Testing
```
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