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    Algorithms and Programs

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    imrayyantube

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    Algorithms and Programs

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    imrayyantube
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    5 views25 pages

    Algorithms and Programs

    Uploaded by

    imrayyantube

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    © All Rights Reserved
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    of 25

    Chapter 03

    Computational Thinking
    Algorithms and Programs
    Slides by
    Ms. Abeera Sikandar
    lecturer
    bahria college anchorage
    computer sciences
    What is an algorithm
    It is a process/procedure that should be followed for some output.
    Program requirement
    The requirement tells you what the program must do.
    For example:
    Calculating a total by adding ten numbers input by the user.
    Start simple
    A good method is to start with a simple version of the problem. A
    programmer might make a program that solves the simple
    problem.
    For example:
    Calculate a total by adding one number input by the user.
    Plan the variables
    The program must have variables. They will store the values.

    Scratch has ready-made variable called answer. It is ‘light blue’


    sensing blocks.
    It store the values input by user.
    Another variable of ‘total’ will be needed to store result of total.
    It has value ‘0’ first.
    Create an algorithm
    Algorithm: set of steps needed to solve a problem.
    It works as a plan when you make a program.
    Create program
    Using scratch program, we’ll create a program now.
    • make a variable
    • Set the value of the variable
    • Use ‘ask’ block to get input
    • Use operators to add and join values.
    • Use ‘say’ block for program input.
    Loop
    Now extend the program to ‘ten’ numbers input.
    Program wants to add a series of numbers.
    Purpose: It needs to do same task over and over again.
    Loop is a program structure which will iterate number of
    times.
    Loop
    Several types of loop from scratch are shown.
    When there is a set limit, like 10 numbers to be added,
    ‘counter’ or ‘fixed’ loop will be used.
    Revised algorithm
    Previous Algorithm Revised Algorithm
    Revised program
    Previous Program Revised Program
    Deliberate mistake:
    Uncover the error:
    Sequence:
    How to save time:
    Writing a computer program is a lot of work. So programmers reuse and repurpose their program.
    • Reuse: means using the same program for a new task.
    For example, program to calculate bill in restaurant will be same as program to calculate
    bill in supermarket.

    • Repurpose: means making some changes to a program so it does a new thing.


    For example, program to add 17% sales tax to an invoice can be repurposed to add 10 %
    service charges to invoice.
    Advantages of reuse & repuporse:

    1. Saves time and work: it takes less time and work to make a small
    change in a program, rather than writing a whole new program.
    2. Less risk of an error: Repurposing the program is less risky than
    writing a new program.
    3. Teamwork: Sharing program with others is good teamwork.
    New requirement
    Program to calculate average of numbers from total.
    How to turn an algorithm into a program
    Combining algorithms
    Programs you have made
    How to combine features you’ve made
    1. Programs to count inputs

    2. Add borrowed commands


    How to combine features you’ve made
    2. Add borrowed commands
    QUIZ: COMBINING FEATURES OF PROGRAMS
    Match each line of code with relevant
    block of scratch
    Set total to 0
    Set counter to 0
    Repeat until answer = X
    Input a number
    Set total to total + answer
    Set counter to counter + 1
    Output the total
    Set average to total/counter
    Output average
    Output counter

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