Introduction to Programming

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Introduction to Programming

• Algorithms

Andreas Savva
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What is an algorithm?

• An Algorithm is a detailed sequence of simple
  steps that are needed to solve a problem.
• It is a step-by-step solution to a problem.

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Mathematical Example

• Problem What is the value of x in the following
  equation?
• 5x 10 30
• Algorithm (Solution)
• Step 1 5x 30 10
• Step 2 5x 40
• Step 3 x 40/5
• Step 4 x 8

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Making a cake

• Step 1 Preheat oven to 200 degrees.
• Step 2 Mix the eggs with the sugar.
• Step 3 Add the butter, flour, and the rest of
  the ingredients.
• Step 4 Stir for 5 minutes.
• Step 5 Put the mixture into a baking pan and
  cook it in a 175 degrees for 40 minutes.
• Step 6 Keep it in the pan for 15 minutes to cool
  down.
• Step 7 Serve with vanilla ice-cream.

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Algorithms
Algorithm Step 1 Move 3 squares and turn
right. Step 2 Move 1 square and turn left. Step
3 Move 2 squares and turn left. Step 4 Move 2
squares and turn right. etc.




































The Problem How will the robot go to the file
folder?
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Representation of Algorithms

• Verbal representation
• Pseudo-code
• Flowchart

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Verbal representation of Algorithms

• Example Write an algorithm to read and calculate
  the average of three numbers.
• Algorithm
• Step 1 Ask for the first number.
• Step 2 Ask for the second number.
• Step 3 Ask for the third number.
• Step 4 Add the three numbers to find their sum.
• Step 5 Divide the sum by 3.
• Step 6 Display the result.

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Flowcharts- graphical representation of an
algorithm
Start Finish
Input Output
Processing
Sub-programs (Separate flowchart)
Choice Statements (Question, Decision)
Comments

• Flow

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Flowchart
Start
Read a
Read b
Read c
Sum ? a b c
Average ? Sum / 3
Display Average
Finish
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Structures

• For the solution of a problem we use three basic
  structures
• Sequential structure
• Conditional structure
• Repetitive structure

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Example 2

• Write an algorithm to read two numbers and
  display the appropriate message if the two
  numbers are equal or not.
• Read a.
• Read b.
• If a b then display that the two numbers are
  equal.
• Else display that the two numbers are NOT equal.

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Start
Conditional Structure
Read a
Read b
a b ?
TRUE
FALSE
Display The two numbers are not equal
Display The two numbers are equal
Finish
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Example 3

• Write an algorithm to read two numbers a and b
  and find the sum of all the numbers between a and
  b inclusive. i.e.
• a 3, b 7, Sum 3 4 5 6 7 25
• a 1, b 100, Sum 1 2 3 100 5,050
• Read a, b
• Sum ? 0
• Counter ? a
• If Counter gt b then Goto 8
• Sum ? Sum Counter
• Counter ? Counter 1
• Goto 4
• Display Sum

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Start
Repetitive Structure
Read a, b
Sum ? 0 i ? a
i gt b ?
TRUE
FALSE
Sum ? Sum i i ? i 1
Display Sum
Finish
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Exercises

• Design a flowchart for the following problems
• Calculate the weekly salary of an employee, when
  the employee-name, working-hours, and
  rate-per-hour are given. If the working-hours
  exceed 40, the rate-per-hour is double than the
  normal hour.
• Given 4 numbers X1, X2, X3, and X4, find and
  display the smaller one.
• Given two numbers A and B. Calculate and display
  the remainder of their division BA. (Hind Keep
  subtracting A from B until you find a smaller
  number than A. i.e. for the division 206 it will
  be 20 6 14 14 6 8 8 6 2 so
  Remainder 2).