2Object-Oriented Program Development Using C++ 3 Basic Loop Structures Loops repeat execution of an...

2Object-Oriented Program Development Using C++


Basic Loop Structures

• Loops repeat execution of an instruction set• Three repetition structures: while, for, do-while• Three common elements

– Test condition controls repetition

– Statement initializes state of test condition

– Internal statement terminates loop

• Syntax variations around placement/type of test


Pretest and Posttest Loops

• Pretest (entrance-controlled) loop– Condition tested before loop statements executed

– Examples: while and for statements

• Posttest (exit-controlled) loop– Termination condition tested at end of loop

– Loop guaranteed to execute at least once

– Example: do-while

• Infinite loop: results from improper update of test


Figure 6-1A Pretest Loop


Figure 6-2A Posttest Loop


Fixed-Count versus Variable-Condition Loops

• Fixed-count loop: condition tracks number of repetitions

• Variable condition loop: test depends on changing variable

• All C++ repetition structures adaptable to either type


while Loops

• Example of while statement: int count = 1; // initialize count

while (count <= 10){

cout << count << endl;

count++; // increment count

}

• Loop turns around value of count• Termination value: count after increment to 11


Figure 6-3Structure of a while Loop


Interactive while Loops

• while statement promotes interactivity• Include interactive prompts and cin statement• Sample program

– Enters and echo-prints four numbers

– Utilizes accumulation statement

– Totals input, computes average, outputs result

• Terminates after fixed count


Figure 6-4Flow of Control for Program 6-5


Figure 6-5Accepting and Adding a Number to a Total


Sentinels

• Sentinels– Values signal start or end of series

– May or may not share data type of input

• Code fragment:cout << "\nTo stop entering numbers, type in any "

<< "number greater than 100" << endl;

while (number <= MAX_COUNT)

• number value greater than 100 terminates loop


break and continue Statements

• break statement– Forces exit from repetition or switch statement

– Syntax: break;

– Most appropriately used in switch statement

• continue statement– Short circuit to next iteration

– Syntax: continue;

– Applies to while, do-while, and for structures


The null Statement

• null statement: consists of a semicolon ( ; ) • Typical use: repetition structure without loop body• Example

– for (int count = 1; count <= pow(10,7) ; count++);

– Time delay loop requires no explicit action


for Loops

• for loop: while functionality with alternate syntax

• Syntax template:for (initializing list; expression; altering list){

statement(s);

}

• Three components between parentheses optional

• Initialization, test, and update conveniently clustered

• Commas separate additional items added to component


Figure 6-7for Loop Control


Figure 6-8Simplified for Loop Flowchart


Nested Loops

• Nested loops: loops within other control structures– Add dimensionality to data

• Code fragmentfor (int i = 1; i <= 10; i++){ // start outer loop

for (int j = 1; j <=10; j++){ // start inner loop

cout << asterisk << space;

} // end inner loop

} // end outer loop

• Inner loop completes 10 x 10 (100) iterations


do-while loops

• do-while loops– Iterates while condition true

– Ends when posttest condition evaluates to false

– Loop guaranteed to execute at least once

• Syntax template:do{

statement(s);

}while (expression);


Figure 6-10The do-while Loop Structure


Figure 6-11The do-while Statement's Flow of Control


Validity Checks

• do-while structure well suited to error handling• Code fragment:

do{

cout << "An invalid grade was just entered\n";

cout << "Please check the grade and re-enter\n";

cin >> grade;

}while (grade < MIN_GRADE || grade > MAX_GRADE);

• If loop entered, guaranteed to execute at least once


Program Design and Development: UML State Diagrams

• State diagram: represents object states over time• Critical design step: specify events that change state• Event

– Signal (or stimulus) from one object to another

– Example: press button to move elevator

• Basic notation– Flow line: denotes event

– State: rectangle with rounded corners


Figure 6-12The State Model Identifies Operations to Be Included in the Class Diagram


Figure 6-13State Diagram Notation


• Objects communicate via messages• Event attributes

– Data values in message– Translate to method arguments

• Action of event: occurs in zero time (instantaneously)• Activity of object: response takes place over time• Examples

– Action: push door bell (or elevator) button – Activity: chimes sound (or elevator moves to floor)

Program Design and Development: UML State Diagrams (continued)


Figure 6-15An Example of an Event Activity


Figure 6-16A State with an Activity


Figure 6-18A State Diagram for an Elevator


Applications: Random Numbers and Simulations

• Many models include statistical/probabilistic elements• Computers support models with random numbers• Random numbers

– Set of numbers whose order cannot be predicted

– Pseudorandom numbers: approximate random condition

• General purpose C++ method: rand ( )


Scaling

• rand ( ) may be adapted to floating-point data• rand ( ) may be modified to scale data values

– Typical scaled range: 0.0 to 1.0– Technique

• Cast return expression to floating-point type• Divide result by RAND_MAX (compiler dependent)

• rand ( ) may be used to return remainders– a + rand( ) % b – a and b represent end-points of interval


Simulations

• Simulations– Computer programs imitating scientific experiment

– Produce important research results

– Avoid overhead associated with experiments

• Random numbers used extensively in simulations


Coin Toss Simulation

• Hypothesis: head as likely as tail (probability = .5)• Coin toss algorithm

– Generates random number between 0 and 1 n times

– If random number >= .5, increment heads (else tails)

• Class diagram– Instance variables: heads and tosses

– Main methods: flip ( ) and percentages ( )

• Results close to projections (difference < .5%)


Figure 6-22A Class Diagram for a CoinToss Class


Elevator Simulation• State diagram

– Action: pressing button– Activity: move to floor (iterative)

• Class diagram– Two attributes: currentFloor and maxFloor– Four methods

• request ( ) performs primary service– Evaluates floor request and moves to same– Uses selection and repetition structures

• Driver enhanced with do-while encasing


Figure 6-23A State Diagram for an Elevator


Figure 6-24A Class Diagram for an Elevator Class


Summary

• Basic repetition structures: while, for, and do-while• Basic loop components: initialization, test, termination• Interactive I/O improved with repetition structures• Nesting: combining structures for complex computation• UML state diagram: event driven


Summary (continued)

• Action: associated with event• Activity: response associated with object• rand ( ) method generates random numbers• Random numbers simulate statistical/probabilistic

patterns• Example simulations: coin toss and elevator

movement

2Object-Oriented Program Development Using C++ 3 Basic Loop Structures Loops repeat execution of an...

Documents

Transcript of 2Object-Oriented Program Development Using C++ 3 Basic Loop Structures Loops repeat execution of an...