Algorithm

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Algorithm Flowchart
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An informal definition of an algorithm is
Algorithm a step-by-step method for solving a
problem or doing a task.
Figure 8.1 Informal definition of an algorithm
used in a computer
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Algorithm

• A step-by-step problem-solving procedure
• An algorithm is a sequence of unambiguous
  instructions for solving a problem.
• The number of steps of an algorithm will be
  countable and finite.
• It is a sequence of instructions (or set of
  instructions) to make a program more readable a
  process used to answer a question.

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• Understand the problem.
• Define the problem
• Analyze the problem
• Develop an algorithm/method of solution
• Write a computer program corresponding to the
  algorithm
• Test and debug the program
• Document the program (how it works and how to use
  it)

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• There are two commonly used tools to help to
  document program logic (the algorithm). These are
  
• Flowcharts
• Pseudo code.

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Flowchart
A flowchart is a type of diagram that represents
an algorithm or process, showing the steps as
boxes of various kinds and their order by
connecting these with arrows. This diagrammatic
representation can give a step-by-step solution
to a given problem.
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• Process operations are represented in these
  boxes, and arrows connecting them represent flow
  of control. Flowcharts are used in analyzing,
  designing, documenting or managing a process or
  program in various fields.

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• Symbols
• Start and end symbols, represented as lozenges,
  ovals or rounded rectangles, usually containing
  the word "Start" or "End", or another phrase
  signaling the start or end of a process, such as
  "submit enquiry" or "receive product".
• Arrows, showing what's called "flow of control"
  in computer science. An arrow coming from one
  symbol and ending at another symbol signifies
  flow passes to the symbol the arrow points to.
• Processing steps, represented as rectangles.
  Examples "Add 1 to X" "replace identified
  part" "save changes" or similar.
• Input/Output, represented as a parallelogram.
  Examples Get X from the user display X.
• Conditional (or decision), represented as a
  diamond (rhombus). These typically contain a
  Yes/No question or True/False test .

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Start or end of the program
Computational steps or processing function of a program
Input or output operation
Decision making and branching
Connector or joining of two parts of program

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1- Simple sequential Flowchart
Example 1

• - Read X, Y, Z
• Compute Sum (S) as X Y Z
• Compute Average (A) as S / 3
• Compute Product (P) as
• X xYxZ
• - Write (Display) the Sum,Average and Product

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• Example 2
• Find the sum of two numbers.
• Variables
• A First Number
• B Second Number
• C Sum (AB)
• Algorithm
• Step 1 Start
• Step 2 Input A
• Step 3 Input B
• Step 4 Calculate C A B
• Step 5 Output C
• Step 6 Stop

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Example 3 Find the difference and the
division of two numbers and display the result
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• Example 4
• Find the circle area and circumcenter of a
  circle where R (radius) is given (exercise)
• Variables
• R Radius
• A Area
• C Circumcenter
• Algorithm
• Step 1 Start
• Step 2 Input R
• Step 3 Calculate Pi
• Step 4 Calculate A Pi(R)2
• Step 5 Calculate C 2Pi(R)
• Step 6 Print R, A, C
• Step 7 Stop

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2- Branched Flowcharts

• Example 1
• Draw a flowchart that shows the traffic light
  processing (exercise)
• Algorithm
• Step 1 Start
• Step 2 make a Decision (what is the color)
• Step 3 if the color is Red then STOP
• Step 4 if the color is Yellow then WAIT
• Step 5 if the color is Green then PASS
• Step 6 Stop

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3- Loop Flowcharts

• Example 1

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Example 2 Average for 10 numbers