1. Programming Fundamentals (750113) Ch1. Problem Solving

2. Programming Fundamentals --> Ch1. Problem solving
Programming is a process of problem solving (Problem Solution by computer)
Algorithm ?
Step-by-step problem-solving process
Solution achieved in finite amount of time
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3. Problem Solving Process
Phase 1 - Analyze the problem
Outline the problem and its requirements
Design (algorithm) to solve the problem ( Flow chart, pseudo code)
Algorithm tracing
Phase 2 - Implement the algorithm
Implement the algorithm in code (in Programming Language  Program)
Verify that the algorithm works
Phase 3 - Maintenance
Use and modify the program if the requirements changes
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4. Programming Fundamentals --> Ch1. Problem solving
Analyze the Problem (1)
Outline the problem and its requirements
Understand the problem
Understand problem requirements
Does program require user interaction?
Does program manipulate data?
What is the output?
are all possible circumstances handled?
If the problem is complex, divide it into subproblems
Analyze each subproblem as above
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5. Programming Fundamentals --> Ch1. Problem solving
Analyze the Problem (1)
Design Algorithm
Flowcharts
pseudo-code
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6. Programming Fundamentals --> Ch1. Problem solving
A Flowchart is
An algorithm graphical representation.
Written as a combination of the following graphical notations:
Flow Chart Symbols
Start and End
Selection
Data Flow
Input / output
Calculation
Programming Fundamentals --> Ch1. Problem solving

7. Programming Fundamentals --> Ch1. Problem solving
Pseudo-code:
<Algorithm name>
// input ? The comment lines “//”
// function?
// Output?
Begin
<data definition>
<actions>
End
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8. Programming Fundamentals --> Ch1. Problem solving
Analyze the Problem (1)
Algorithm Tracing
Draw flowchart
Find all possible paths
Check each path with appropriate input data
Observed Outputs not conform to the expected ones  error in the algorithm.
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9. Programming Fundamentals --> Ch1. Problem solving
Analyze the Problem (2)
Problem Example.
Convert a student mark from decimal mode to ABC mode.
Understand problem requirements
Is the problem statement complete and unambiguous?
Does program require user interaction? Input the mark
Does program manipulate data?  covert mark
What is the output? The mark converted to A or B or C or error
Is there subproblem? No
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10. Programming Fundamentals --> Ch1. Problem solving
Analyze the Problem (2)
Efficiency:
- an algorithm may work correctly but be inefficient – by taking more time and using more resources than required to solve the problem.
- becomes more important for larger programs.
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11. Programming Fundamentals --> Ch1. Problem solving
Analyze the Problem (3)
Design Algorithm  Algorithm Discovery
To discover an algorithm is to solve the problem!
Working backwards (modification of an old solution)
Example: Min of a and b is known. Deduce Max a and b.
Look for a related problem that has been solved before (similar solutions reuse)
The precedent algorithm of mark conversion is for single student. It may be generalized to many students
Stepwise Refinement (new solution)
Break the problem into several sub-problems
Solve each subproblem separately
Produces a modular structure
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12. Programming Fundamentals --> Ch1. Problem solving
Analyze the Problem (3)
Example. Making tea. Suppose we have a robot which carries out household tasks. We wish to program the robot to make a cup of tea. An initial attempt at an algorithm might be:
1. Put tea leaves in pot
2. Boil water
3. Add water to pot
4. Wait 5 minutes
5. Pour tea into cup
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13. Programming Fundamentals --> Ch1. Problem solving
Analyze the Problem(3)
Design Algorithm  Algorithm Discovery Strategies  Stepwise Refinement
These steps are probably not detailed enough for the robot. We
therefore refine each step into a sequence of smaller steps:
1. Put tea leaves in pot might be refined to
1.1 Open box of tea
1.2 Extract one spoonful of tea leaves
1.3 Tip spoonful into pot
1.4 Close box of tea
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14. Programming Fundamentals --> Ch1. Problem solving
Analyze the Problem(3)
Design Algorithm  Algorithm Discovery Strategies  Stepwise Refinement
2. Boil water might be refined to
2.1. Fill kettle with water
2.2 Switch on kettle
2.3 Wait until water is boiled
2.4 Switch off kettle
…..
5. Pour tea into cup might be refined to
5.1. Pour tea from pot into cup until cup is full
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16. Programming Fundamentals --> Ch1. Problem solving
Analyze the Problem(3)
the designer must know when to stop refining.
In this example the instruction Switch on kettle is directly executable by the robot, but that Fill kettle with water is not.
Experience will tell us when a step is directly implementable or not.
The above algorithm consists of a sequence of steps, executed exactly once and in order
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17. Programming Fundamentals --> Ch1. Problem solving
Analyze the Problem(3)
What happens if the tea-box is empty?
Control Requirements: IF
If the tea-box is empty we wish to specify an extra step:
Get new box of tea from cupboard
— This step would not be carried out unless the tea-box is empty,
We can express this by rewriting step 1.1 as
Take tea box from shelf
If box is empty
then get new box from cupboard
Remove lid from box
— Step expresses both the step to be selected and the
condition under which this selection should be made.
More complicated conditions can use AND, OR, NOT
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18. Programming Fundamentals --> Ch1. Problem solving
Analyze the Problem(3)
Control requirements: while
Another common requirement is the need for iteration.
— Example. Repeat the mark conversion for a class room of 30 students. Each student having a unique student number from 1 to 30.
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19. Implement the algorithm
Use any programming language (C++) to write a program to solve the problem. Where program is a sequence of statements.
Use any programming language (C++) to write a program to solve the problem. Where program is a sequence of statements.
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20. Programming Fundamentals --> Ch1. Problem solving
Computer Stage: after completing the program, the computer must do the following:
Compilation: the computer compile the program. If it has errors, then an error list is produced to be corrected by the programmer.
Execution: when the program become don’t has errors, the computer execute it to produce the ……output.
Programming Fundamentals --> Ch1. Problem solving

21. Implement the algorithm
Verify that the algorithm works  source of errors
Many errors made in:
analyzing the problem,
developing an algorithm, and/or
coding the algorithm
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22. Implement the algorithm
• Errors are of three types:
. syntax errors
. run-time errors
. logic errors
• Syntax errors: detected by the C compiler
. source code does not conform to one or more of C’s grammar rules
. examples of syntax errors: undeclared variable, …
• Often one mistake leads to multiple error messages – can be confusing
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23. Implement the algorithm
• Run-time errors. detected and displayed by computer during execution.
- Occur when program directs computer to perform illegal operation. Example: int x=y/0;
- will stop program execution and display message
• Logic errors.
- caused by faulty algorithm
- sign of error: incorrect program output
cure: thorough testing and comparison with expected results
A logic error is referred to as a bug, so finding logic errors is called debugging.
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24. Programming Fundamentals --> Ch1. Problem solving
Conclusions (Cont’d)
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