Chapter 2 - Controld Structures

2000 Prentice Hall, Inc. All rights reserved.

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Chapter 2 - Control StructuresOutline2.1 Introduction2.2 Algorithms2.3 Pseudocode2.4 Control Structures2.5 The if Selection Structure2.6 The if/else Selection Structure2.7 The while Repetition Structure2.8 Formulating Algorithms: Case Study 1

(Counter-Controlled Repetition)2.9 Formulating Algorithms with Top-Down, Stepwise Refinement:

Case Study 2 (Sentinel-Controlled Repetition)2.10 Formulating Algorithms with Top-Down, Stepwise Refinement:

Case Study 3 (Nested Control Structures)2.11 Assignment Operators2.12 Increment and Decrement Operators2.13 Essentials of Counter-Controlled Repetition2.14 The for Repetition Structure2.15 Examples Using the for Structure


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Chapter 2 - Control StructuresOutline2.16 The switch Multiple-Selection Structure2.17 The do/while Repetition Structure2.18 The break and continue Statements2.19 Logical Operators2.20 Confusing Equality (==) and Assignment (=) Operators2.21 Structured-Programming Summary


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2.1 Introduction

• Before writing a program:– Have a thorough understanding of problem – Carefully plan your approach for solving it

• While writing a program: – Know what “building blocks” are available– Use good programming principles


4Fundamental Building Blocks of Programs

• THERE ARE TWO BASIC ASPECTS of programming:– data and instructions.

• To work with data– you need to understand variables and types

• To work with instructions– you need to understand control structures and subroutines. – You'll spend a large part of the course becoming familiar

with these concepts

Ref: http://math.hws.edu/javanotes/c1/s4.html


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A few good programming practices• Be consistent with formatting.

– Use proper spacing and indentation– There's nothing worse than code that is difficult to read because it

is poorly formatted. • Be consistent with naming conventions

– Chose one naming style and stick with it • Use global variables sparingly

– Avoid them as much as possible• Comment. Add comments to your code in plain English

that describe both what the code is doing and why you decided to do it one way and not another way Ref:

• Check return values for error conditions • Provide useful error messages. • Recover (or fail) gracefully. http://www.kmoser.com/articles/

Good_Programming_Practices.php

int main()

{

if ( num1 == num2 )

cout << num1 << " is equal to " << num2 << endl;

if ( num1 != num2 )

cout << num1 << " is not equal to " << num2 << endl;

}

int main()

{ if (num1==num2)

cout<<num1<<" is equal to "<<num2<<endl;

if (num1!=num2)

cout<<num1<<" is not equal to " <<num2<<endl; }

A well formtated piece of code

A poorly formtated piece of code


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2.2 Algorithms

• All computing problems– can be solved by executing a series of actions in a specific

order

• Algorithm– A procedure determining the

• Actions to be executed • Order in which these actions are to be executed

• Program control– Specifies the order in which statements are to executed


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The Algorithm to Start the Car

1.Insert the key2.Make sure car is in neutral gear3.Press the gas pedal/ (Accelerator)4.Turn the key to the start position5.If the engine starts in 6 seconds

1.Release the key to the ignition position6.Else if the engine does not start in 6 seconds

1.Release the key and gas pedal2.Wait for 10 seconds , and repeat the steps 3 – 6, but no more

than 5 times7. If the car does not start

1.Call the workshop


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2.3 Pseudocode

• Pseudocode– Artificial, informal language used to develop algorithms– Similar to everyday English– Not actually executed on computers – Allows us to “think out” a program before writing the code

for it– Easy to convert into a corresponding C++ program– Consists only of executable statements

Example:

If student’s grade is greater than or equal to 60

Print "Passed“


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2.4 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

• Bohm and Jacopini: all programs written in terms of 3 control structures– Sequence structure

• Built into C++. Programs executed sequentially by default.– Selection structures

• C++ has three types - if, if/else, and switch – Repetition structures

• C++ has three types - while, do/while, and for


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2.4 Control Structures

• C++ keywords– Cannot be used as identifiers or variable names.C++ Keywords

Keywords common to the C and C++ programming languages

auto break case char const continue default do double else enum extern float for goto if int long register return short signed sizeof static struct switch typedef union unsigned void volatile while C++ only keywords

asm bool catch class const_cast delete dynamic_cast explicit false friend inline mutable namespace new operator private protected public reinterpret_cast static_cast template this throw true try typeid typename using virtual wchar_t


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2.4 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 beginning or end of a program, or a section of code (circles).

– Diamond symbol (decision symbol)• indicates decision is to be made

• 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.


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2.5 The if Selection Structure

• Selection structure– used to choose among alternative courses of action– Pseudocode example:

If student’s grade is greater than or equal to 60Print “Passed”

– If the condition is true• print statement executed and program goes on to next

statement– If the condition is false

• print statement is ignored and the program goes onto the next statement

– Indenting makes programs easier to read• C++ ignores whitespace characters


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• Translation of pseudocode statement into C++:if ( grade >= 60 ) cout << "Passed";

• Diamond symbol (decision symbol)– indicates decision is to be made– Contains an expression that can be true or false.

• Test the condition, follow appropriate path

• if structure is a single-entry/single-exit structure


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• Flowchart of pseudocode statement

true

false

grade >= 60

print “Passed”

A decision can be made on any expression.

zero - false

nonzero - true

Example:

3 - 4 is true


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2.6 The if/else Selection Structure• if

– Only performs an action if the condition is true• if/else

– A different action is performed when condition is true and when condition is false

• Psuedocodeif student’s grade is greater than or equal to 60

print “Passed”else

print “Failed”

• C++ codeif ( grade >= 60 ) cout << "Passed";else cout << "Failed";


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2.6 The if/else Selection Structure

• C++ codeif ( grade >= 60 ) cout << "Passed";else cout << "Failed";

truefalse

print “Failed” print “Passed”

grade >= 60


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• Ternary conditional operator (?:)– Takes three arguments (condition, value if true, value if false)

• Our pseudocode could be written:cout << ( grade >= 60 ? “Passed” : “Failed” );

truefalse

print “Failed” print “Passed”

grade >= 60


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Ternary conditional operator • Nested if/else structures

– Test for multiple cases by placing if/else selection structures inside if/else selection structures.

if student’s grade is greater than or equal to 90 Print “A”else if student’s grade is greater than or equal to 80 Print “B” else if student’s grade is greater than or equal to 70

Print “C” else if student’s grade is greater than or equal to 60

Print “D” else

Print “F”– Once a condition is met, the rest of the statements are skipped


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2.6 The if/else Selection Structure• Compound statement:

– Set of statements within a pair of braces– Example:

if ( grade >= 60 ) cout << "Passed.\n";else { cout << "Failed.\n"; cout << "You must take this course again.\n";}

– Without the braces,cout << "You must take this course again.\n"; would be automatically executed

• Block– Compound statements with declarations


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• Syntax errors– Errors caught by compiler

• Logic errors– Errors which have their effect at execution time

• Non-fatal logic errors– program runs, but has incorrect output

• Fatal logic errors– program exits prematurely


21The switch Multiple-Selection Statement

• switch– Useful when a variable or expression is tested for all the values it

can assume and different actions are taken• Format

– Series of case labels and an optional default caseswitch ( value ){

case '1':actions

case '2':actions

default:actions

}– break; // exits from statement


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Same actions taken for two casesswitch ( value ){

case '1':case '2':

actions /* one or more statements */break;

case '3':case '4':


default:actions /* one or more statements */break;

}


232.16The switch Multiple-Selection Structure• switch

– Useful when variable or expression is tested for multiple values– Consists of a series of case labels and an optional default case

true

false

.

.

.

case a case a action(s) break

case b case b action(s) break

false

falsecase z case z action(s) break

true

true

default action(s)


242.7 The while Repetition Structure

• Repetition structure– Programmer specifies an action to be repeated while some

condition remains true– Psuedocode

while there are more items on my shopping list Purchase next item and cross it off my list

– while loop repeated until condition becomes false.

• Exampleint product = 2;while ( product <= 1000 ) product = 2 * product;


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2.7 The while Repetition Structure

• Flowchart of while loop

product <= 1000 product = 2 * producttrue

false


262.8 Formulating Algorithms (Counter-Controlled Repetition)

• Counter-controlled repetition– Loop repeated until counter reaches a certain value.

• Definite repetition– Number of repetitions is known

• Example A class of ten students took a quiz. The grades (integers in

the range 0 to 100) for this quiz are available to you. Determine the class average on the quiz.


272.8 Formulating Algorithms (Counter-Controlled Repetition)

• Pseudocode for example:Set total to zero

Set grade counter to one

While grade counter is less than or equal to ten

Input the next grade

Add the grade into the total

Add one to the grade counter

Set the class average to the total divided by ten

Print the class average

• Following is the C++ code for this example

total = 0

gradeCounter = 1

while (gradeCounter ≤ 10)

input grade

total = total + gradegradeCounter = gradeCounter + 1

average = total / 10

Print average


Outline4

16 // initialization phase

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1. Initialize Variables

2. Execute Loop

3. Output results

1 // Fig. 2.7: fig02_07.cpp2 // Class average program with counter-controlled repetition3 #include <iostream.h>

9 int main()10 {11 int total, // sum of grades 12 gradeCounter, // number of grades entered13 grade, // one grade

17 total = 0; // clear total18 gradeCounter = 1; // prepare to loop

20 // processing phase21 while ( gradeCounter <= 10 ) { // loop 10 times

22 cout << "Enter grade: "; // prompt for input23 cin >> grade; // input grade24 total = total + grade; // add grade to total25 gradeCounter = gradeCounter + 1; // increment counter26 }28 // termination phase29 average = total / 10; // integer division30 cout << "Class average is " << average << endl;3132 return 0; // indicate program ended successfully33 }

The counter gets incremented each time the loop executes. Eventually, the counter causes the loop to end.

14 average; // average of grades


Outline29

Program Output

Enter grade: 98Enter grade: 76Enter grade: 71Enter grade: 87Enter grade: 83Enter grade: 90Enter grade: 57Enter grade: 79Enter grade: 82Enter grade: 94Class average is 81


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2.9 Formulating Algorithms with Top-Down, Stepwise Refinement (Sentinel-Controlled Repetition)

• Suppose the problem becomes: Develop a class-averaging program that will process an arbitrary number of grades each time the program is run.

– Unknown number of students - how will the program know to end?

• Sentinel value– Indicates “end of data entry”– Loop ends when sentinel is inputted – Sentinel value chosen so it cannot be confused with a regular

input (such as -1 in this case)


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2.9 Formulating Algorithms with Top-Down, Stepwise Refinement (Sentinel-Controlled Repetition)

• Top-down, stepwise refinement– begin with a pseudocode representation of the top:

Determine the class average for the quiz

– Divide top into smaller tasks and list them in order:

Initialize variablesInput, sum and count the quiz gradesCalculate and print the class average


322.9 Formulating Algorithms with Top-Down, Stepwise Refinement

• Many programs can be divided into three phases: – Initialization

• Initializes the program variables– Processing

• Inputs data values and adjusts program variables accordingly– Termination

• Calculates and prints the final results. • Helps the breakup of programs for top-down refinement.

• Refine the initialization phase fromInitialize variables

toInitialize total to zeroInitialize counter to zero

Recall the program to control average grade of the class

total = 0

gradeCounter = 1



• Refine Input, sum and count the quiz grades

to

Input the first grade (possibly the sentinel) While the user has not as yet entered the sentinel

Add this grade into the running total Add one to the grade counter Input the next grade (possibly the sentinel)

• RefineCalculate and print the class average

to If the counter is not equal to zero

Set the average to the total divided by the counter Print the average

Else Print “No grades were entered”

Processing step

Termination step

while continue

input grade

total = total + gradegradeCounter = gradeCounter + 1

average = total / 10

Print average

input grade

grade ! =0 ?


Outline

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19

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1. Initialize Variables

2. Get user input

2.1 Perform Loop

1 // Fig. 2.9: fig02_09.cpp2 // Class average program with sentinel-controlled repetition.3 #include <iostream.h>4 #include <iomanip.h>5 int main()6 {7 int total, // sum of grades8 gradeCounter, // number of grades entered9 grade; // one grade 10 float average; // number with decimal point for average12 // initialization phase13 total = 0;14 gradeCounter = 0;

16 // processing phase17 cout << "Enter grade, -1 to end: "; 18 cin >> grade;

20 while ( grade != -1 ) {

Data type float used to represent decimal numbers.

21 total = total + grade; 22 gradeCounter = gradeCounter + 1; 23 cout << "Enter grade, -1 to end: "; 24 cin >> grade;

25 }


Outline35

3. Calculate Average

3.1 Print Results

Program Output

2627 // termination phase28 if ( gradeCounter != 0 ) { 29 average = (float )( total ) / gradeCounter;30 cout << "Class average is " << setprecision( 2 )31 << setiosflags( iostream::fixed | iostream::showpoint )32 << average << endl;33 }34 else35 cout << "No grades were entered" << endl;3637 return 0; // indicate program ended successfully38 }

Enter grade, -1 to end: 75Enter grade, -1 to end: 94Enter grade, -1 to end: 97Enter grade, -1 to end: 88Enter grade, -1 to end: 70Enter grade, -1 to end: 64Enter grade, -1 to end: 83Enter grade, -1 to end: 89Enter grade, -1 to end: -1Class average is 82.50

(float)(total) - treats total as a double temporarily.

Required because dividing two integers truncates the remainder.

gradeCounter is an int, but it gets promoted to double.

=-iostream::fixed | iostream::showpoint) - stream manipulator

iostream::fixed - output numbers with a fixed number of decimal points.

iostream::showpoint - forces decimal point and trailing zeros, even if unnecessary: 66 printed as 66.00

| - separates multiple option.

setprecision(2) - prints only two digits past decimal point.

Programs that use this must include <iomanip.h>


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Before you start coding

• Ensure your algorithm is correct.

• How is that done?

• One way is to “Dry Run” your algorithm.


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Dry Run

• “…a dry run is a mental run of an algorithm, sometimes expressed in pseudocode, where the computer scientist examines the algorithm's procedures one step at a time.”

(Source: Wikipedia)

• Use pen and paper to keep track of variable values during a dry run.



Input the first gradeWhile the user has not as yet entered the

sentinel Add this grade into the running total Add one to the grade counter Input the next grade (possibly the sentinel)


Outline39

2.10 Nested control structures• Problem:

– A college has a list of test results (1 = pass, 2 = fail) for 10 students.

– Write a program that analyzes the results. • If more than 8 students pass, print "Raise Tuition".

• We can see that– The program must process 10 test results

A counter-controlled loop will be used. – Two counters can be used—

• one to count the number of students who passed the exam and• one to count the number of students who failed the exam.

– Each test result is a number— either a 1 or a 2. If the number is not a 1, we assume that it is a 2.


Outline40

2.10 Nested control structures

• Top level outline:Analyze exam results and decide if tuition should be raised

• First Refinement:Initialize variables

Input the ten quiz grades and count passes and failuresPrint a summary of the exam results and decide if tuition should be raised

• RefineInitialize variables

to Initialize passes to zeroInitialize failures to zeroInitialize student counter to one

passes = 0

failures = 0

studentCounter = 1


Outline41

2.10 Nested control structures• Refine

Input the ten quiz grades and count passes and failures to

While student counter is less than or equal to tenInput the next exam resultIf the student passed Add one to passesElse Add one to failuresAdd one to student counter

• RefinePrint a summary of the exam results and decide if tuition should be raised

toPrint the number of passesPrint the number of failuresIf more than eight students passed

Print “Raise tuition”

while ( studentCounter ≤ 10 )input result

If (result = 1)passes = passes + 1

failures = failures + 1studentCounter =studentCounter+ 1

Else

Print passesPrint failuresif passes > 8

Print “Raise tuition


Outline42

1. Initialize variables

2. Input data and count passes/failures

1 // Fig. 2.11: fig02_11.cpp

2 // Analysis of examination results

3 #include <iostream.h>4 int main()

5 {

6 // initialize variables in declarations

7 int passes = 0, // number of passes

8 failures = 0, // number of failures

9 studentCounter = 1, // student counter

10 result; // one exam result

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12 // process 10 students; counter-controlled loop

13 while ( studentCounter <= 10 ) {

14 cout << "Enter result (1=pass,2=fail): ";

15 cin >> result;

16

17 if ( result == 1 ) // if/else nested in while

18 passes = passes + 1;19 else20 failures = failures + 1;2122 studentCounter = studentCounter + 1;23 }


Outline43

3. Print results

Program Output

2425 // termination phase26 cout << "Passed " << passes << endl;27 cout << "Failed " << failures << endl;2829 if ( passes > 8 )30 cout << "Raise tuition " << endl;3132 return 0; // successful termination33 }

Enter result (1=pass,2=fail): 1Enter result (1=pass,2=fail): 1Enter result (1=pass,2=fail): 1Enter result (1=pass,2=fail): 1Enter result (1=pass,2=fail): 2Enter result (1=pass,2=fail): 1Enter result (1=pass,2=fail): 1Enter result (1=pass,2=fail): 1Enter result (1=pass,2=fail): 1Enter result (1=pass,2=fail): 1Passed 9Failed 1Raise tuition


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2.11Assignment Operators

• Assignment expression abbreviationsc = c + 3; can be abbreviated as c += 3; using the

addition assignment operator

• Statements of the formvariable = variable operator expression;

can be rewritten asvariable operator= expression;

• Examples of other assignment operators include:d -= 4 (d = d - 4)e *= 5 (e = e * 5)f /= 3 (f = f / 3)g %= 9 (g = g % 9)


452.12Increment and Decrement Operators

• Increment operator (++) - can be used instead of c += 1

• Decrement operator (--) - can be used instead of c -= 1– Preincrement

• When the operator is used before the variable (++c or ––c)• Variable is changed, then the expression, it is in, is evaluated.

– Posincrement• When the operator is used after the variable (c++ or c--)• Expression the variable is in executes, then the variable is changed.

• If c = 5, then – cout << ++c; prints out 6 (c is changed before cout is

executed)– cout << c++; prints out 5 (cout is executed before the

increment. c now has the value of 6)


462.12Increment and Decrement Operators

• When Variable is not in an expression– Preincrementing and postincrementing have the

same effect.++c; cout << c;

and c++; cout << c;

have the same effect.

If c was originally 5

What will be Output ?

6


47Some Examples – Nested Loop

- Nested While Loop1. Write a program to print a triangle of ‘*’

– Use 2 counters, one each for row counter and column counter– Each time the columns will start from one, so the counter for

column must be initialized inside the first while loop– The row counter and column count have be increment inside first

while and outside second while (except the column counter)

2. Practice questions- print a square of ‘*’ using nested while loop, rows and column are given.- Print a triangle as above but use sentinel repetition control

***************


48Some Examples - Operators#include<iostream.h>#include<conio.h>void main(){int a = 5; int b= 6;int c = (a++) + (b++); clrscr();cout<<"\na = "<<a;cout<<"\nb = "<<b;cout<<"\nc = "<<c;

int x=4; int y=4;int z = (x++) - (--y);cout<<"\n\nx = "<<x;cout<<"\ny = "<<y;cout<<"\nz= "<<z;

a = 6b = 7c = 11

x = 5y = 3z =1

Screen Output

the summation result is stored

in c before the post increments

z = (x++) – (--y)

--y = 3

z = 4 – 3 = 1

x++ = 5

c = (a++) + (b++)

c = a + b = 5 + 6 = 11

a++ = 6

b++ = 7


49Some Examplesint k; float f;x = 5; y = 3;cout<<"\n\nx/y = "<<x/y;f = x/y;cout<<"\n\nf = x/y = "<<f;k = (float)(x/y);cout<<"\n\nk = (float)(x/y) = "<<k;f = (float)(x/y);cout<<"\n\nf = (float)(x/y)= "<<f;cout<<"\n\n(float)(x/y) = "<<(float)(x/y);cout<<"\n\n(float)x /y = "<<(float)x /y;cout<<"\n\n1.5 /3 = "<< 1.5/3;cout<<"\n\n1/3.0 = "<< 1/3.0;getch();}

x/y = 1

f = x/y = 1

k = (float)(x/y) = 1

f = (float)(x/y) = 1

(float)(x/y) = 1

(float)x /y = 1.6666667

1.5/3 = 0.5

1/3.0 = 0.333333

Screen Output


502.13Essentials of Counter-Controlled Repetition

• Counter-controlled repetition requires:– The name of a control variable (or loop counter).– The initial value of the control variable.– The condition that tests for the final value of the control

variable (i.e., whether looping should continue).– The increment (or decrement) by which the control variable is

modified each time through the loop. – Body (optional)

• Example: int counter =1; //initializationwhile (counter <= 10){ //repetition condition cout << counter << endl; ++counter; //increment

}


512.13Essentials of Counter-Controlled Repetition

• The declarationint counter = 1;

– Names counter– Declares counter to be an integer– Reserves space for counter in memory– Sets counter to an initial value of 1


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2.14The for Repetition Structure

• The general format when using for loops isfor ( initialization; LoopContinuationTest;

increment )

statement • Example:

for( int counter = 1; counter <= 10; counter++ )cout << counter << endl;

– Prints the integers from one to ten

No semicolon after last statement


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2.14The for Repetition Statement

for( int counter = 1; counter <= 10; counter++ )

for keyword Control variable name Final value of the control variable for the condition is true

Increment of control variable

Loop-continuation condition

Initial value of control variable


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2.14The for Repetition Structure• for loops can usually be rewritten as while loops:

initialization;while ( loopContinuationTest){ statement increment;}

• Initialization and increment as comma-separated listsfor (int i = 0, j = 0; j + i <= 10; j++, i++) cout << j + i << endl;


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2.14The for Repetition Statement

• Format when using for loopsfor ( initialization; loopContinuationTest; increment )

statement----------------------------------------------------------------------------------------

for ( initialization; loopContinuationTest; increment ) { statement1 statement2.. statementN

}

• Example: for( int counter = 1; counter <= 10; counter++ ) cout<<“\n“<< counter;

– Prints the integers from one to ten

No semicolon (;) after last expression


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Recap: The while Repetition Structure

• Flowchart of while loop

product <= 1000 product = 2 * producttrue

false


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The for Statement :

counter = 1

counter <= 10true

false

counter = 1

counter++

Establish initial value of control variable

Determine if final value of control variable has been reached

Body of loop (this may be many statements)

Increment the control variable

Cout<<“\n” <<counter ;

counter <= 10true

false

Cout<<“\n” <<counter ;counter++

while Statement

counter = 1 Initialization placed before the while statement

Counter integrated into the body of while statement


Outline58

fig04_02.c

1 /* Fig. 4.2: fig04_02.c 2 Counter-controlled repetition with the for statement */ 3 #include <iostream.h> 4 5 /* function main begins program execution */ 6 int main() 7 { 8 int counter; /* define counter */ 9 10 /* initialization, repetition condition, and increment 11 are all included in the for statement header. */ 12 for ( counter = 1; counter <= 10; counter++ ) { 13 cout<<”\n” << counter ; 14 } /* end for */ 15 16 return 0; /* indicate program ended successfully */ 17 18 } /* end function main */


592.14The for Statement : Notes and Observations

• Arithmetic expressions– Initialization, loop-continuation, and increment can contain

arithmetic expressions. If x equals 2 and y equals 10 for ( j = x; j <= 4 * x * y; j += y / x )

is equivalent tofor ( j = 2; j <= 80; j += 5 )

• Notes about the for statement:– "Increment" may be negative (decrement)– If the loop continuation condition is initially false

• The body of the for statement is not performed• Control proceeds with the next statement after the for statement

– Control variable• Often printed or used inside for body, but not necessary


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The for Statement :

counter = 1

counter <= 10true

false

counter = 1

counter++

Establish initial value of control variable

Determine if final value of control variable has been reached

Body of loop (this may be many statements)

Increment the control variable

Cout<<“\n” <<counter ;


61

2.15Examples Using the for Structure

1 // Fig. 2.20: fig02_20.cpp2 // Summation with for

3 #include <iostream.h>4

78 int main()9 {10 int sum = 0;1112 for ( int number = 2; number <= 100; number += 2 )13 sum += number;1415 cout << "Sum is " << sum << endl;1617 return 0;18 }

Sum is 2550

• Program to sum the even numbers from 2 to 100


Outline62

fig04_06.c (Part 1 of 2)

1 /* Fig. 4.6: fig04_06.c 2 Calculating compound interest */ 3 #include <iostream.h> 4 #include <math.h> 5 6 /* function main begins program execution */ 7 int main() 8 { 9 double amount; /* amount on deposit */ 10 double principal = 1000.0; /* starting principal */ 11 double rate = .05; /* interest rate */ 12 int year; /* year counter */ 13 14 /* output table column head */ 15 cout<< "Year \t Amount on deposit" ; 16 17 /* calculate amount on deposit for each of ten years */ 18 for ( year = 1; year <= 10; year++ ) { 19 20 /* calculate new amount for specified year */ 21 amount = principal * pow( 1.0 + rate, year ); 22 23 /* output one table row */ 24 cout<< year<<” \t ” << amount ; 25 } /* end for */ 26


Outline63

fig04_06.c (Part 2 of 2)

Program Output

Year Amount on deposit 1 1050.00 2 1102.50 3 1157.63 4 1215.51 5 1276.28 6 1340.10 7 1407.10 8 1477.46 9 1551.33 10 1628.89

27 return 0; /* indicate program ended successfully */ 28 29 } /* end function main */

21 character places

04 character places


642.17The do/while Repetition Structure

• The do/while repetition structure is similar to the while structure, – Condition for repetition tested after the body of the loop is

executed• Format:

do { statement} while ( condition );

• Example (letting counter = 1): do {cout << counter << " ";

} while (++counter <= 10);– This prints the integers from 1 to 10

• All actions are performed at least once.

true

false

action(s)

condition


2.17The do…while Repetition Statement

• Flowchart of the do…while repetition statement

true

false

action(s)

condition


2.17 COMPARISON: The while Repetition Statement

• Flowchart of the while repetition statement

true

false

action(s)condition


672.18The break and continue Statements

• Break– Causes immediate exit from a while, for, do/while or switch structure

– Program execution continues with the first statement after the structure

– Common uses of the break statement:• Escape early from a loop• Skip the remainder of a switch structure


1 2 Using the break statement in a for statement */ 3 #include <io.streamh> 4 5 /* function main begins program execution */ 6 int main() 7 { 8 int x; /* counter */ 9 /* loop 10 times */ 10 for ( x = 1; x <= 10; x++ ) { 11 /* if x is 5, terminate loop */ 12 if ( x == 5 ) { 13 break; /* break loop only if x is 5 */ 14 } /* end if */ 15 cout<< x; /* display value of x */ 16 } /* end for */ 17 cout<< "\nBroke out of loop at x == \n" << x ; 18 return 0; /* indicate program ended successfully */

1 2 3 4Broke out of loop at x == 5


692.18The break and continue Statements

• Continue– Skips the remaining statements in the body of a while, for or do/while structure and proceeds with the next iteration of the loop

– In while and do/while, the loop-continuation test is evaluated immediately after the continue statement is executed

– In the for structure, the increment expression is executed, then the loop-continuation test is evaluated


1 2 Using the continue statement in a for statement */ 3 #include <stdio.h>

5 /* function main begins program execution */ 6 int main() 7 { 8 int x; /* counter */ 10 /* loop 10 times */ 11 for ( x = 1; x <= 10; x++ ) { 13 /* if x is 5, continue with next iteration of loop */ 14 if ( x == 5 ) { 15 continue; /* skip remaining code in loop body */ 16 } /* end if */ 18 cout<< "%d "<< x ; /* display value of x */ 19 } /* end for */ 21 cout<< "\nUsed continue to skip printing the value 5\n"; 23 return 0; /* indicate program ended successfully */

25 } /* end function main */

fig04_12.c

Program Output

1 2 3 4 6 7 8 9 10Used continue to skip printing the value 5


71

2.19Logical Operators• && (logical AND)

– Returns true if both conditions are true• || (logical OR)

– Returns true if either of its conditions are true• ! (logical NOT, logical negation)

– Reverses the truth/falsity of its condition– Returns true when its condition is false– Is a unary operator, only takes one condition

• Logical operators used as conditions in loops Expression Resulttrue && false falsetrue || false true!false true


722.20Confusing Equality (==) and Assignment (=) Operators

• These errors are damaging because they do not ordinarily cause syntax errors.– Recall that any expression that produces a value can be used in

control structures. Nonzero values are true, and zero values are false

• Example:if ( payCode == 4 ) cout << "You get a bonus!" << endl;

– Checks the paycode, and if it is 4 then a bonus is awarded• If == was replaced with =

if ( payCode = 4 ) cout << "You get a bonus!" << endl;

– Sets paycode to 4– 4 is nonzero, so the expression is true and a bonus is awarded,

regardless of paycode.


732.20Confusing Equality (==) and Assignment (=) Operators

• Lvalues– Expressions that can appear on the left side of an equation– Their values can be changed– Variable names are a common example (as in x = 4;)

• Rvalues– Expressions that can only appear on the right side of an

equation– Constants, such as numbers (i.e. you cannot write 4 = x;)

• Lvalues can be used as rvalues, but not vice versa


Operator precedence examples 74


752.16The switch Multiple-Selection Statement

• switch– Useful when a variable or expression is tested for all the

values it can assume and different actions are taken

• Format– Series of case labels and an optional default case

switch ( value ){case '1':

actionscase '2':

actionsdefault:

actions}

– break; exits from statement


76

Same actions taken for two cases

switch ( value ){case '1':case '2':


case '3':case '4':


default:actions /* one or more statements */break;

}


772.16The switch Multiple-Selection Structure

• switch– Useful when variable or expression is tested for multiple values– Consists of a series of case labels and an optional default case

true

false

.

.

.

case a case a action(s) break

case b case b action(s) break

false

false

case z case z action(s) break

true

true

default action(s)


78

1. Initialize variables

2. Input data

2.1 Use switch loop to update count

1 // Fig. 2.22: fig02_22.cpp2 // Counting letter grades3 #include <iostream.h>456789 int main()10 {11 int grade, // one grade12 aCount = 0, // number of A's13 bCount = 0, // number of B's14 cCount = 0, // number of C's15 dCount = 0, // number of D's16 fCount = 0; // number of F's1718 cout << "Enter the letter grades." << endl19 << "Enter the EOF character to end input." << endl;2021 while ( ( grade = cin.get() ) != EOF ) {2223 switch ( grade ) { // switch nested in while2425 case 'A': // grade was uppercase A26 case 'a': // or lowercase a27 ++aCount; 28 break; // necessary to exit switch2930 case 'B': // grade was uppercase B31 case 'b': // or lowercase b32 ++bCount; 33 break;34

Notice how the case statement is used


79

2.1 Use switch loop to update count

3. Print results

35 case 'C': // grade was uppercase C36 case 'c': // or lowercase c37 ++cCount; 38 break;3940 case 'D': // grade was uppercase D41 case 'd': // or lowercase d42 ++dCount; 43 break;4445 case 'F': // grade was uppercase F46 case 'f': // or lowercase f47 ++fCount; 48 break;4950 case '\n': // ignore newlines, 51 case '\t': // tabs, 52 case ' ': // and spaces in input53 break;5455 default: // catch all other characters56 cout << "Incorrect letter grade entered."57 << " Enter a new grade." << endl;58 break; // optional59 }60 }6162 cout << "\n\nTotals for each letter grade are:" 63 << "\nA: " << aCount 64 << "\nB: " << bCount 65 << "\nC: " << cCount 66 << "\nD: " << dCount67 << "\nF: " << fCount << endl;6869 return 0;70 }

break causes switch to end and the program continues with the first statement after the switch structure.

Notice the default statement.


80

Program Output

Enter the letter grades.Enter the EOF character to end input.aBcCAdfCEIncorrect letter grade entered. Enter a new grade.DAb Totals for each letter grade are: A: 3B: 2C: 3D: 2F: 1


812.17The do/while Repetition Structure

• The do/while repetition structure is similar to the while structure, – Condition for repetition tested after the body of the loop is

executed• Format:

do { statement} while ( condition );

• Example (letting counter = 1): do {cout << counter << " ";

} while (++counter <= 10);– This prints the integers from 1 to 10

• All actions are performed at least once.

true

false

action(s)

condition


2.17The do…while Repetition Statement

• Flowchart of the do…while repetition statement

true

false

action(s)

condition


2.17 COMPARISON: The while Repetition Statement

• Flowchart of the while repetition statement

true

false

action(s)condition


842.21Structured-Programming Summary

• Structured programming– Programs are easier to understand, test, debug and, modify.

• Rules for structured programming– Only single-entry/single-exit control structures are used– Rules:

1) Begin with the “simplest flowchart”.2) Any rectangle (action) can be replaced by two rectangles

(actions) in sequence. 3) Any rectangle (action) can be replaced by any control

structure (sequence, if, if/else, switch, while, do/while or for).4) Rules 2 and 3 can be applied in any order and multiple times.



Rule 3

Rule 3Rule 3

Representation of Rule 3 (replacing any rectangle with a control structure)



• All programs can be broken down into– Sequence– Selection

• if, if/else, or switch • Any selection can be rewritten as an if statement

– Repetition• while, do/while or for• Any repetition structure can be rewritten as a while

statement


Nested for loop

• for(num2 = 0; num2 <= 3; num2++){ for(num1 = 0; num1 <= 2; num1++) { cout<< num2<< " " << num1<< endl; }}

87

http://mathbits.com/mathbits/compsci/looping/nested.htm


Nested for loop

for(num2 = 0; num2 <= 3; num2++){ for(num1 = 0; num1 <= 2; num1++) { cout<< num2<< " " << num1<< endl; }}

88

http://mathbits.com/mathbits/compsci/looping/nested.htm

Chapter 2 - Controld Structures

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