Slide 1
Programming
Dr Damitha KarunaratnaSenior LecturerUniversity of Colombo
School of [email protected]
UCSC Algorithms/Flow Charts What is an algorithm?Different ways
of representing algorithms.What is a computer program?Main steps in
solving a problem by using computer programs. How can an algorithm
converted into a computer program?
2UCSC What is an algorithm? An algorithm is a step-by-step
procedure (a finite number of steps) for solving a problem.
AssumptionsObjectiveStarting pointProcessTerminal point(s)Algorithm
to get ready to come to school.
2UCSCDifferent ways of representing algorithmsFlow charts
Graphical representationPseudo code Text representationA great deal
of pseudo code is a blend of simple imperative constructs and
English
4UCSCSymbols used in Flow
chartsProcessDecisionInput/OutputTerminatorConnectorFlowDirection5UCSCIncorrect
Flow charts ????Is remainder(X/2) = 0 ?Read a number (X)Start6The
number is oddThe number is evenA Flow chart to determine whether a
given number is odd or evenUCSCIncorrect Flow chartsY = remainder
(x/2)Is y = 0?Read a number (X)Start7StopDisplay The number is
oddDisplay The number is evenA Flow chart to determine whether a
given number is odd or evenyesNoUCSCHow to encode a flow chart as a
program ? Must know the various constructs provided by the
language.Reserved wordsFlow control mechanisms
SequencingSelectionRepetition
(Iteration/Loops)Decompose(disintegrate) a program into a
collection of subprograms (procedures)8UCSC Flow Charts - Selection
Types of Flow Control StatementsIF ..ThenElse .End IfNest IF Select
Case End Select
19
UCSC Flow Charts - Repetition Types of Flow Control
StatementsFor..NextDo..While conditionDo..Until condition
Loops110
UCSCIF .. ThenElseCondition?Statement 1Statement 3Statement 2One
course-of-actionAnother course-of-actionTrueFalse11
UCSCIF .. ThenElse - ExampleTrueFalseIF a Student obtained at
least 50 marks he will pass the Exam , otherwise
Fail.Marks>=50?Get Student Marks Print Pass the Exam Print Fail
the Exam12UCSCIF .. ThenElse : Example Pseudo CodeGet Student Mark
(M) IF (M>=50) Then Display/Print PassELSE Display/Print
FailENDIF13UCSCNested IF ExampleIF a Student obtained more than 80
marks he will get a Distinction else If he obtained more than or
equal to 50, he will pass else will Fail. 14UCSC14Nested IF -
ExampleMarks>80?TrueFalseMarks>=50?TrueFalse Print
Distinction Print FailPrint PassGet Marks15UCSCNested IF -
ExampleMarks>=50?TrueFalseMarks>80?TrueFalse Print Pass Print
FailPrint DistinctionGet Marks16This part will never get
executedUCSCIF .. ThenElse : Example Pseudo CodeGet Student Mark
(M) IF (M>80) THEN Display DistinctionELSE IF (M>=50) THEN
Display Pass ELSE Display Fail ENDIFENDIF17UCSCSelect Case End
SelectCase can evaluate only one variable whereas Nest IF can
evaluate multiple variables.No special Flow chart symbol
18UCSC18Select Case End Select Example - Pseudo CodeGet Student
Mark (M) Select Case ( M)Case 0 To 49 Display FailCase 50 To 80
Display PassCase Else Display Distinction END Select19UCSCIterative
Statements Loops20
Condition can be at the end of the loop
While conditionStatement(s)TrueFalseI = 1Do Print I I = I +
1Loop while I < 5UCSC20Iterative Statements Loops21
Or Condition can be at the start of the loop
While conditionStatement(s)TrueFalseI = 1Do while I < 5 Print
I I = I + 1Loop UCSC21Iterative Statements LoopsFalse22
Statement (s)Statement(s) (s)Do WhileEnd DoTrueStatement(s)
(s)Statement (s)Statement (s)Do UntilEnd DoTrueStatement
(s)FalseUCSC22Iterative Statements For NextFor I= 1 To 5 Print I
Next II=1I=I+1 I
