CS149D Elements of Computer Science

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CS149D Elements of Computer Science
Ayman Abdel-Hamid Department of Computer
Science Old Dominion University Lecture 18
10/31/2002
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Outline

• Finish Chapter 2
• Mathematical and Trigonometric functions
• Example page 48
• Chapter 3
• Flowcharts
• Program Structures
• Conditional expressions
• Selection Statements

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Mathematical/Trigonometric functions
include ltmath.hgt Argument is a double and return
value a double fabs(x) absolute value of
x sqrt(x) square root of x pow (x,y) x to the
power of y ceil (x) ceiling (3.1)
4 floor(x) floor (3.99) 3 see page 46 for
more functions
include ltmath.hgt Argument is a double and return
value a double, angles are represented in radians
(180 PI radians) sin(x) cos(x)
tan(x,y) see page 47 for more functions
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Example
Example page 48 Velocity Computation Velocity
0.00001 time3-0.00488time20.75795time181.3566 Ac
celeration 3 0.000062 velocity2 See program
on page 51
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Chapter 3

• Flowcharts as a tool for algorithm representation
• Control structures (selection, repetition)
• Data Files

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Flowchart Symbols
Operation Pseudocode Input Read
radius Computation Assign area the value PI
radius2 Output Write (or Print) radius,
area Comparisons if radius lt 0 then Begin/End
Area PI radius2
Is radius lt 0 ?
Yes
No
Start/Stop
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Program Structures1/3
Sequence structure Steps that are performed one
after another (all programs so far) Flowchart for
the triangle area program
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Program Structures2/3
Selection structure Contains a condition that
evaluates to either true or false If condition is
true one set of statements is executed, otherwise
(if false) another set of statements is executed
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Program Structures3/3
Repetition structure Repeat a set of steps as
long as a condition is true Print x2 for x
0,1,., 9
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Conditional Expressions

• A condition is an expression that can be
  evaluated to true or false
• Composed of expressions combined with relational
  and logical operators
• Relational operators ( lt, lt, gt, gt, , !)
• a lt b
• a 10 b 2 a lt b evaluates to false
• a 2 b 10 a lt b evaluates to true
• a b gt c If b gt c then a is assigned 1
  otherwise assigned 0
• Logical operators ( ! (NOT), (AND), (OR))
• a lt b b lt c (a less than b) AND (b less than
  c)
• a is 2, b is 9, c is 2 condition evaluates to
  false (Why?)
• Relational operators have higher precedence than
  logical operators. See precedence table page 67

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Selection Statements1/2
A statement can be a compound statement if
(condition) Statement 1 .. Statement
n Example if (A lt 10) B 5 A C 2
if (condition) Statement 1 Example if ( A lt
10) B 5 C 2
if/else statement if (condition) Statement
1 else Statement 2 Example if ( A lt 10) B
5 else C 2
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Selection Statements2/2
if ( A lt 10) B 5 else C 2 D 3
Nested ifs if (x gt y) if (y lt z) K else M el
se J Compiler always matches else with closest
if
Nested ifs if (x gt y) if (y lt z) K else J Wh
en J gets executed?