1. Problem Solving Skill Area 305.1
Materials Prepared by Dhimas Ruswanto, BMm
Skill Area 305.1
Problem Solving

2. Lecture Overview
Problem Solving
Algorithm
Dry Run

3. PROBLEM SOLVING Problem-Solving methodology: Define the problem
Outline the solution
Develop an algorithm
Test the algorithm

4. DEFINE THE PROBLEM Have a thorough understanding of the problem
State the problem in clear and concise terms to avoid any confusion or misunderstanding
Examples: Calculate the
sum and the average
of two numbers 25 & 45

5. OUTLINE THE SOLUTION The problem can be divided into three components:
Inputs – What do you have?
Outputs – What do you want to have?
Processing – How do you go from inputs to outputs?
Examples: Calculate the sum and the average of two numbers 25 & 45

6. OUTLINE THE SOLUTION (cont’d)
Inputs =
First number = a = 25
Second number = b = 45
Outputs =
sum
average
Processing =
sum = a +b
Average = a+b 2

7. ALGORITHM
An algorithm is a written step by step solution to a problem.
Why bother writing an algorithm?
For your own use in the future. You won’t have to rethink the problem.
So others can use it, even if they know very little about the principles behind how the solution was derived

8. ALGORITHM (cont’d)
An algorithm is a finite set of unambiguous, executable instructions that directs a terminating activity.
GOAL: To find a single set of instructions that can be used to solve any problem of a particular type (a general solution).

9. EXAMPLE OF ALGORITHM
MAKE A CALL

10. EXAMPLES OF ALGORITHM

11. ALGORITHM REPRESENTATION
Syntax:
The grammar of the language
The way in which we construct sentences by following principles and rules
Semantics:
The meaning
The interpretations of and meanings derived from the sentence transmission and understanding of the message

12. SYNTAX AND SEMANTIC Sentence : “Baby milk drinks”
Does not have a syntactic meaning
But through semantics most people would interpret it as meaning “Baby drinks milks”, therefore we can find a meaning from key words.

13. SYNTAX AND SEMANTIC (CONT’D)
In programming language:
Syntax defines how logical entities expressed in characters
Semantics describe the logical entities of a programming language and their interactions
Examples:
x = 0 - 1; y = - 1;
the syntax for the "-" token is the same, but, it has a different meaning ("semantic), depending where its used.
In the "x" assignment, "-" means the "subtraction" operation, In the "y" assignment, "-" means the "negative sign" operation.

14. DEVELOP AN ALGORITHM
Decompose the problem into simpler steps and expresses the solution in terms of
actions to be executed
order in which these actions are to be executed
Examples: Calculate the sum and the average of two numbers 25 & 45

15. DEVELOP AN ALGORITHM (CONT’D)
Declare two variables, a and b
Initialise both variables to 0
a= 0, b= 0
Ask user to enter first number
Assign user input to a variable
Ask user to enter second number
Assign user input to second b variable
Add first num to second num
Print the sum
Divide the sum by 2
Print the average

16. TEST THE ALGORITHM
The programmer must make sure that the algorithm is correct.
The objective is to identify major logic errors early, so that they may be easily corrected.
Test data should be applied to each step, to check whether the algorithm actually does what it is supposed to.

17. DRY RUN
You can test your program without using a computer by dry running it on paper
Dry runs involves the execution of code segments.
You act as the computer – following the instructions of the program, recording the valves of the variables at each stage
You can do this with a table

18. DRY RUN (Cont’d)
The table with have column headed with the names of the variables in the program
Each row in the table will be labelled with a line number form the program.
The entries of each row in the table will be values of the variables after the execution of the statement on that line
You don’t need a row for every line in the program, just those lines where some significant change to the state of the program occurs
e.g a variable gets a new value

19. DRY RUN (Cont’d)
In this table you can record all relevant changes to the variables as the program progresses, thereby test the logic of the program / algorithm
Do a dry run before you code your program on computer this way any logic errors will come to light during the dry run

20. Example of DRY RUN L1 Declare two variables, a and b
L2 Initialise both variables to 0
L3 a= 0, b= 0
L4 Ask user to enter first number
L5 Assign user input to a variable
L6 Ask user to enter second number
L7 Assign user input to second b variable
L8 Add first num to second num
L9 Print the sum
L10 Divide the sum by 2
L11 Print the average
Do a Dry run for this program assuming the user enters 18 for first number and 24 for the second

21. A Sample of DRY RUN table
After
execution
First num
Second num
Sum
Average
Line 2
Line 5 18
Line 7 24
Line 8 42
Line 10 21

22. SUMMARY
An algorithm is a finite set of unambiguous, executable instructions that directs a terminating activity.
Syntax:
The grammar of the language
Semantics:
The meaning
Dry runs involves the execution of code segments.