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Department of Computer and Information Science, School of Science, IUPUI. Program Control using Java - Theory. Dale Roberts, Lecturer Computer Science, IUPUI E-mail: [email protected] Algorithms. Algorithms is the are part of the problem solving process ‘A’ in ST A IR.

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Program Control using Java - Theory

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Program control using java theory l.jpg

Department of Computer and Information Science,School of Science, IUPUI

Program Control using Java- Theory

Dale Roberts, Lecturer

Computer Science, IUPUI

E-mail: [email protected]


Algorithms l.jpg

Algorithms

  • Algorithms is the are part of the problem solving process

    • ‘A’ in STAIR.

    • All computing problems can be solved by executing a series of actions in a specific order, called an algorithm

  • Algorithm: procedure in terms of

    • Actions to be executed

    • The order in which these actions are to be executed

  • Program control

    • Specify order in which statements are to executed


Definition of algorithm l.jpg

Definition of Algorithm

  • Definition of an Algorithm

    • consists of unambiguous & computable operations

    • produce a result

    • halt in a finite amount of time.

    • Some scientists add a restriction that the algorithm must halt in a reasonable amount of time. Why would there be resistance to this idea?


Control structures l.jpg

Control Structures

  • Sequential execution

    • Statements executed one after the other in the order written

  • Transfer of control

    • When the next statement executed is not the next one in sequence

    • Overuse of goto statements led to many problems

  • Bohm and Jacopini

    • All programs written in terms of 3 control structures

      • Sequence structures: Built into C. Programs executed sequentially by default

      • Selection structures: Java has three types: if, if/else, and switch

      • Repetition structures: Java has three types: while, do/while and for


Pseudocode l.jpg

Pseudocode

  • Pseudocode

    • An informal language similar to English

    • Helps programmers develop algorithms

    • Does not run on computers

    • Should contain input, output and calculation actions

    • Should not contain variable declarations

For each student i in the Class

Calculate the student’s average score

If the average score >= 90A% Then

Assign Student[i] grade to ‘A’

End if

End For


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Control Structures

  • Sequential execution

    • Statements are normally executed one after the other in the order in which they are written

  • Transfer of control

    • Specifying the next statement to execute that is not necessarily the next one in order

    • Can be performed by the goto statement

      • Structured programming eliminated goto statements


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4.4  Control Structures (Cont.)

  • Bohm and Jacopini’s research

    • Demonstrated that goto statements were unnecessary

    • Demonstrated that all programs could be written with three control structures

      • The sequence structure,

      • The selection structure and

      • The repetition structure


4 4 control structures cont8 l.jpg

4.4  Control Structures (Cont.)

  • UML activity diagram (www.uml.org)

    • Models the workflow (or activity) of a part of a software system

    • Action-state symbols (rectangles with their sides replaced with outward-curving arcs)

      • represent action expressions specifying actions to perform

    • Diamonds

      • Decision symbols (explained in Section 4.5)

      • Merge symbols (explained in Section 4.7)


Control structures9 l.jpg

Control Structures

  • Flowchart

    • Graphical representation of an algorithm

    • Drawn using certain special-purpose symbols connected by arrows called flowlines

    • Rectangle symbol (action symbol):

      • Indicates any type of action

    • Oval symbol:

      • Indicates the beginning or end of a program or a section of code

  • Single-entry/single-exit control structures

    • Connect exit point of one control structure to entry point of the next (control-structure stacking)

    • Makes programs easy to build


4 4 control structures cont10 l.jpg

4.4  Control Structures (Cont.)

  • Small circles

    • Solid circle represents the activity’s initial state

    • Solid circle surrounded by a hollow circle represents the activity’s final state

  • Transition arrows

    • Indicate the order in which actions are performed

  • Notes (rectangles with the upper-right corners folded over)

    • Explain the purposes of symbols (like comments in Java)

    • Are connected to the symbols they describe by dotted lines


Fig 4 1 sequence structure activity diagram l.jpg

Fig. 4.1 | Sequence structure activity diagram.


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Acknowledgements

  • Deitel, Java How to Program


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