Transcript Define the problem (Analysis)

Software Development
1. Define the problem (Analysis)
2. Plan the solution
3. Code
4. Test and debug
5. Maintain and Document
sw development
1
Code
• Write program in a specified language
• editor - key in- create source program
– .cpp (if c++ is the language)
• compiling - create object program
– Syntax error
– .obj
• link - create executable
– .exe
• Run
– Logic errors
• Lab #1
sw development
2
Problem Analysis
•
1.
2.
3.
4.
5.
Problems: Take one of the following tasks and write a set
of instructions(a solution) so complete that another
person could perform the task without asking questions
Make a cup of cocoa
Sharpen a pencil
Decide which number is the largest from a group of
three numbers
Start a car(include directions regarding what to do if the
car does not start
Buy a soda from the soda machine
sw development
3
Problem Solving
• Identify, understand the problem
• Obtain additional information
• Read and reread to obtain additional
information
• Alternatives
• List instructions that enable you to solve the
problem by the selected method
sw development
4
Problem Solving
• Some problems require a series of actions or an
algorithmic colution
– Exa. solving a complicated calculus program
– Alphabetizing 10,000 names
• Other problems require reasoning built on
knowledge and experience – heuristic solution
• Computers are better at algorithmic solutions
• Problems with problem solving
– Define problem incorrectly
– Don't identify a sufficient list of alternatives
sw development
5
Analysis of the Problem
1. Determine what is given - input
=>nouns, adjectives
2. Determine what is required - output
=>nouns, adjectives
3. Determine the transformations
needed(processing)
-actions needed to produce the required output
=>verbs, adverbs
sw development
6
Example 1:
Read three numbers, add them together and print the total.
Read three numbers, add them together and print the total.
Input
Processing
Output
Read three numbers
total
number_1
Add numbers together
number_2
Print total number
number_3
sw development
7
Example 2:
Write a program to prompt the operator for the maximum and
minimum temperature readings on a particular day, accept those
readings as integers, and calculate and display on the screen the
average temperature.
Input
max_temp
Processing
Output
Prompt for temps
avg_temp
Calculate average
min_temp
Display average
sw development
8
Structured Programming
• Control structures
– sequence
– selection or IF-THEN-ELSE
– repetition or looping
– subprograms
• Top Down Design
• Modularity
sw development
9
Design/Plan the solution
• Algorithm – a step by step procedure for solving
a problem
• All programs are implementations of algorithms
– subtasks - hierarchy chart
– logic
• flowcharts
• pseudocode
– test solution for correctness - trace
sw development
10
Algorithm
• Algorithm – set of steps that defines how a
task is performed
• Program – set of instructions written in
appropriate language
– Correctness
– efficiency
sw development
11
Pseudocode
• structured concise English statements used
to state operations
• language independent,no standard
• use words and phrases that are in line with
basic computer operations
sw development
12
Pseudocode
1. Write statements in simple English
2. Write each instruction on a separate line.
3. Use keywords and indentation for control
structures.
4. Write instructions from top to bottom,
with only one entry and one exit.
sw development
13
Pseudocode
1.
Input - receiving information
• keywords - read, get
• Read - receive information from a record on a file
• Get - receive information from the keyboard.
• Read student_name
• Get system_date
• Read number_1,number_2
• Get tax_code
• use one verb followed by one or more nouns
sw development
14
Pseudocode
2. Output
– putting information out
• put, output,display - screen
• print - printer
• write - file
–
–
–
–
–
Print smaller.
Print 'Program Completed'
Write customer_record to file
Output total_tax
Display 'End of Data'
sw development
15
Output continued
• Labels
– Print 'label' or
Print "label"
• statement inside quotes is printed as it appears
– Print 'x'
• Yields
// if x = 5
x
– Print x
• yields
5
– Print 'X = ' and x
• yields:
X=5
sw development
16
Pseudocode
3. Arithmetic
• use name of the operation or algebraic symbol
• add,subtract,multiply, divide, exponentiation
• + - * / **
• x = algebraic expression
–
–
–
–
count = count + 1
net pay = hourly_pay_rate * hours_worked
sales_tax = cost_price * 0.10
sales_tax = price * tax_rate
sw development
17
Pseudocode
4. Assignment - place information into a storage
location
• Initialize, Set - give variable initial value
• Save,Store - save info for later
• =
//preferred
y = 3 note: does not mean equality
– could involve calculation:
– area = length * width
sw development
18
Assignment
• Examples
–
–
–
–
–
–
counter = 0
Initialize counter to zero
Set count to 1
Initialize tot_accums to 0
Set upper_limit to 100
total_price = cost_price + sales_tax
sw development
19