Program Control using Java - Theory

1. Department of Computer and Information Science,School of Science, IUPUI Program Control using Java- Theory Dale Roberts, Lecturer Computer Science, IUPUI E-mail: droberts@cs.iupui.edu

2. 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

3. 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?

4. 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

5. 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

6. 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

7. 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

8. 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)

9. 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

10. 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

11. Fig. 4.1 | Sequence structure activity diagram.

12. Acknowledgements • Deitel, Java How to Program