2003 Prentice Hall, Inc. All rights reserved. 1 Control Structures Outline Assignment Operators Increment and Decrement Operators Essentials of Counter-Controlled

2003 Prentice Hall, Inc. All rights reserved.

1

Control Structures

OutlineAssignment OperatorsIncrement and Decrement OperatorsEssentials of Counter-Controlled Repetitionfor Repetition StructureExamples Using the for Structureswitch Multiple-Selection Structuredo/while Repetition Structurebreak and continue StatementsLogical OperatorsConfusing Equality (==) and Assignment (=) OperatorsStructured-Programming Summary


2

Assignment Operators

• Assignment expression abbreviations– Addition assignment operator

c = c + 3; abbreviated to c += 3;

• Statements of the formvariable = variable operator expression;

can be rewritten asvariable operator= expression;

• Other assignment operatorsd -= 4 (d = d - 4)

e *= 5 (e = e * 5)

f /= 3 (f = f / 3)

g %= 9 (g = g % 9)


3

Increment and Decrement Operators

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

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

• When the operator is used before the variable (++c or –c)

• First, variable is changed, then new value is used in the expression in which it appears.

– Posincrement• When the operator is used after the variable (c++ or

c--)• Expression that the variable is in executes first, then

the variable is changed.


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• Increment operator (++)– Increment variable by one– c++

• Same as c += 1

• Decrement operator (--) similar – Decrement variable by one– c--


5


• If c = 5, then – cout << ++c; // (increment then use)

• c is changed to 6, then printed out

– cout << c++; // (use then increment)• Prints out 5 (cout is executed before the

increment. • c then becomes 6


6


• When variable not in expression– Preincrementing and postincrementing have

same effect++c;

cout << c;

and c++;

cout << c;

are the same

2003 Prentice Hall, Inc.All rights reserved.

Outline7

1 // Fig. 2.14: fig02_14.cpp2 // Preincrementing and postincrementing.3 #include <iostream>4 5 using std::cout;6 using std::endl;7 8 // function main begins program execution9 int main()10 {11 int c; // declare variable12 13 // demonstrate postincrement14 c = 5; // assign 5 to c15 cout << c << endl; // print 516 cout << c++ << endl; // print 5 then postincrement17 cout << c << endl << endl; // print 6 18 19 // demonstrate preincrement20 c = 5; // assign 5 to c21 cout << c << endl; // print 522 cout << ++c << endl; // preincrement then print 6 23 cout << c << endl; // print 6


Outline8

24 25 return 0; // indicate successful termination26 27 } // end function main

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Essentials of Counter-Controlled Repetition

• Counter-controlled repetition requires– Name of control variable/loop counter– Initial value of control variable– Condition to test for final value– Increment/decrement to modify control variable

when looping


Outline10

1 // Fig. 2.16: fig02_16.cpp2 // Counter-controlled repetition.3 #include <iostream>4 5 using std::cout;6 using std::endl;7 8 // function main begins program execution9 int main()10 {11 int counter = 1; // initialization12 13 while ( counter <= 10 ) { // repetition condition14 cout << counter << endl; // display counter15 ++counter; // increment16 17 } // end while 18 19 return 0; // indicate successful termination20 21 } // end function main


Outline11

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• 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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11 int counter = 1; // initialization12 13 while ( counter <= 10 ) { // repetition condition14 cout << counter << endl; // display counter15 ++counter; // increment16 17 } // end while

11 int counter = 0; // initialization12 13 while ( ++counter <= 10 ) // repetition condition14 cout << counter << endl; // display counter1516 17


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for Repetition Structure

• General format when using for loopsfor ( initialization; LoopContinuationTest;

increment )

statement;

• Examplefor( int counter = 1; counter <= 10; counter++ )

cout << counter << endl;

– Prints integers from one to ten


Outline15

1 // Fig. 2.17: fig02_17.cpp2 // Counter-controlled repetition with the for structure.3 #include <iostream>4 5 using std::cout;6 using std::endl;7 8 // function main begins program execution9 int main()10 {11 // Initialization, repetition condition and incrementing 12 // are all included in the for structure header. 13 14 for ( int counter = 1; counter <= 10; counter++ )15 cout << counter << endl; 16 17 return 0; // indicate successful termination18 19 } // end function main


Outline16

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• for loops can usually be rewritten as while loops

initialization;

while ( loopContinuationTest){

statement

increment;

}

• Initialization and increment– For multiple variables, use comma-separated lists

for (int i = 0, j = 0; j + i <= 10; j++, i++)

cout << j + i << endl;


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• The three expressions in the for header are optional:– If the loopContinuationTest is omitted, C++

considers that this condition as true infinite loop

14 for ( int counter = 1; ; counter++ )15 cout << counter << endl; 16


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Outline20

1 // Fig. 2.20: fig02_20.cpp2 // Summation with for.3 #include <iostream>4 5 using std::cout;6 using std::endl;7 8 // function main begins program execution9 int main()10 {11 int sum = 0; // initialize sum12 13 // sum even integers from 2 through 10014 for ( int number = 2; number <= 100; number += 2 ) 15 sum += number; // add number to sum16 17 cout << "Sum is " << sum << endl; // output sum18 return 0; // successful termination19 20 } // end function main

Sum is 2550


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Examples Using the for Structure

for (int i = 1; i <= 100; i++)

// vary control variable from 1 to 100 in increments of 1

for (int i = 100; i >= 1; i--)

// vary control variable from 100 to 1 in increments of -1 (i.e., decremented)

for (int i = 7; i <= 77; i+=7)

// vary control variable from 7 to 77 in steps of 7


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14 for ( int number = 2; number <= 100; number += 2 ) 15 sum = sum + number;

14 for ( int number = 2; 15 number <= 100;

16 number += 2 )

17 sum = sum + number;

14 for ( int number = 2; 15 number <= 100;

16 sum += number, number += 2 )

17 ; // empty body


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• Program to calculate compound interestA person invests $1000.00 in a savings account yielding 5 percent interest. Assuming that all interest is left on deposit in the account, calculate and print the amount of money in the account at the end of each year for 10 years. Use the following formula for determining these amounts:

a = p(1+r) n

• p is the original amount invested (i.e., the principal),r is the annual interest rate,n is the number of years anda is the amount on deposit at the end of the nth year


Outline24

1 // Fig. 5.6: fig05_6.cpp2 // Calculating compound interest.3 #include <iostream>4 5 using std::cout;6 using std::endl;7 using std::ios;8 using std::fixed;9 10 #include <iomanip>11 12 using std::setw; // enables program to set a field width13 using std::setprecision;14 15 #include <cmath> // enables program to use function pow16 17 // function main begins program execution18 int main()19 {20 double amount; // amount on deposit21 double principal = 1000.0; // starting principal22 double rate = .05; // interest rate23


Outline25

24 // output table column heads25 cout << "Year" << setw( 21 ) << "Amount on deposit" << endl;26 27 // set floating-point number format28 cout << fixed << setprecision( 2 ); 29 30 // calculate amount on deposit for each of ten years31 for ( int year = 1; year <= 10; year++ ) {32 33 // calculate new amount for specified year34 amount = principal * pow( 1.0 + rate, year );35 36 // output one table row37 cout << setw( 4 ) << year 38 << setw( 21 ) << amount << endl;39 40 } // end for 41 42 return 0; // indicate successful termination43 44 } // end function main


Outline26

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


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do/while Repetition Structure

• Similar to while structure– Makes “loop continuation test” at end, not

beginning Loop body executes at least once

• Formatdo {

statement

} while ( condition );


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do/while Repetition Structure


Outline29

1 // Fig. 5.7: fig05_7.cpp2 // Using the do/while repetition structure.3 #include <iostream>4 5 using std::cout;6 using std::endl;7 8 // function main begins program execution9 int main()10 {11 int counter = 1; // initialize counter12 13 do { 14 cout << counter << " "; // display counter15 counter++;16 } while (counter <= 10 ); // end do/while 17 18 cout << endl;19 20 return 0; // indicate successful termination21 22 } // end function main

1 2 3 4 5 6 7 8 9 10


Outline30

1 // Fig. 5.7: fig05_7.cpp2 // Using the do/while repetition structure.3 #include <iostream>4 5 using std::cout;6 using std::endl;7 8 // function main begins program execution9 int main()10 {11 int counter = 1; // initialize counter12 13 do { 14 cout << counter << " "; // display counter15 } while ( ++counter <= 10 ); // end do/while 16 17 cout << endl;18 19 return 0; // indicate successful termination20 21 } // end function main

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switch Multiple-Selection Structure

• switch– Test variable for multiple values– Series of case labels and optional default case

switch ( variable ) {case value1: // taken if variable == value1statementsbreak; // necessary to exit switch

case value2:case value3: // taken if variable == value2 or ==

value3statementsbreak;

default: // taken if variable matches no other casesstatementsbreak;

}


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• Example upcoming– Program to read grades (A-F)– Display number of each grade entered

• Details about characters– Single characters typically stored in a char data

type• C++ feature: characters can be stored in any

integer data type because they are represented as 1-byte integers in the computer.


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– Can treat character as int or char• 97 is the numerical representation of lowercase ‘a’

(ASCII)• Use single quotes to get numerical representation

of charactercout << "The character (" << 'a' << ") has the value " << static_cast< int > ( 'a' ) << endl;

PrintsThe character (a) has the value 97

Next: you will see why we chose to represent characters as integers


Outline35

1 // fig02_22.cpp2 // Counting letter grades.3 #include <iostream>4 5 using std::cout;6 using std::cin;7 using std::endl;8 9 // function main begins program execution10 int main()11 {12 int grade; // one grade13 int aCount = 0; // number of As14 int bCount = 0; // number of Bs15 int cCount = 0; // number of Cs16 int dCount = 0; // number of Ds17 int fCount = 0; // number of Fs18 19 cout << "Enter the letter grades." << endl20 << "Enter the EOF character to end input." << endl;21


Outline36

22 // loop until user types end-of-file key sequence23 while ( ( grade = cin.get() ) != EOF ) {24 25 // determine which grade was input26 switch ( grade ) { // switch structure nested in while27 28 case 'A': // grade was uppercase A29 case 'a': // or lowercase a30 ++aCount; // increment aCount31 break; // necessary to exit switch32 33 case 'B': // grade was uppercase B34 case 'b': // or lowercase b35 ++bCount; // increment bCount 36 break; // exit switch37 38 case 'C': // grade was uppercase C39 case 'c': // or lowercase c40 ++cCount; // increment cCount 41 break; // exit switch42


Outline37

43 case 'D': // grade was uppercase D44 case 'd': // or lowercase d45 ++dCount; // increment dCount 46 break; // exit switch47 48 case 'F': // grade was uppercase F49 case 'f': // or lowercase f50 ++fCount; // increment fCount 51 break; // exit switch52 53 case '\n': // ignore newlines, 54 case '\t': // tabs, 55 case ' ': // and spaces in input56 break; // exit switch57 58 default: // catch all other characters59 cout << "Incorrect letter grade entered."60 << " Enter a new grade." << endl;61 break; // optional; will exit switch anyway62 63 } // end switch64 65 } // end while66


Outline38

67 // output summary of results68 cout << "\n\nTotals for each letter grade are:" 69 << "\nA: " << aCount // display number of A grades70 << "\nB: " << bCount // display number of B grades71 << "\nC: " << cCount // display number of C grades 72 << "\nD: " << dCount // display number of D grades73 << "\nF: " << fCount // display number of F grades74 << endl;75 76 return 0; // indicate successful termination77 78 } // end function main


Outline39

Enter the letter grades.

Enter the EOF character to end input.

a

B

c

C

A

d

f

C

E

Incorrect letter grade entered. Enter a new grade.

D

A

b

^Z

Totals for each letter grade are:

A: 3

B: 2

C: 3

D: 2

F: 1


Outline40

1 // GradeBook.h2 // Definition of class GradeBook that counts A, B, C, D and F grrades3 // Member functions are defined in GradeBook.cpp45 #include <string>6 using std::string;78 // GradeBook Class definition9 Class GradeBook10 {11 public:12 GradeBook(string); // constructor initializes courseName 13 void setCourseName(string); // Function that sets the course name14 string getCourseName(); // Function that gets the course name15 void displayMessage(); // Function that displays a welcome message16 void inputGrades(); // input arbitrarily number of grades17 void displayGradeReport(); // display report based on grades18 private:19 string courseName; // course name of this GradeBook 20 int aCount; // count of A Grades21 int bCount; // count of B Grades22 int cCount; // count of C Grades23 int dCount; // count of D Grades24 int fCount; // count of F Grades25 }; // end class GradeBook

Using Classes


411 // GradeBook.cpp2 // Member function definitions for class GradeBook that3 // uses a switch statement to count A, B, C, D, and F grades4 #include <iostream>5 using std::cout; 6 using std::cin; 7 using std::endl; 89 #include “GradeBook.h”10 11 // Constructor initializes courseName with string supplied as argument;12 // initializes counter data members to 0;13 GradeBook::GradeBook(string name)14 { 15 setCourseName(name); //validate and store courseName16 aCount = 0; //initializes count of A grades to 017 bCount = 0; //initializes count of B grades to 018 cCount = 0; //initializes count of C grades to 019 dCount = 0; //initializes count of D grades to 020 fCount = 0; //initializes count of F grades to 021 } // End constructor


4222 23 // function to set the course name; limits names to 25 or fewer characters24 void GradeBook::setCourseName(string name)25 { 26 if (name.length() <= 25) //if name has 25 or fewer characters27 courseName = name; //store name in the courseName28 else 29 courseName = name.substr(0, 25) //select first 25 characters30 } 3132 // Function that gets the course name33 String GradeBook::getCourseName()34 { 35 return courseName; // store the object’s course name36 } // end function getCourseName3738 // Function that displays a welcome message39 void GradeBook::displayMessage()40 { 41 // call getCourseName to get the courseName42 cout << “Welcome to the grade book for\n"<< getCourseName()<<"!“ 43 <<endl;44 } // end function displayMessage


4345 // input arbitrary number of grades 46 void GradeBook::inputGrades()47 { 48 int grade; //grade entered by user49 cout << "Enter the letter grades." << endl50 << "Enter the EOF character to end input." << endl;51 // loop until user types end-of-file key sequence52 while ( ( grade = cin.get() ) != EOF ) {53 54 // determine which grade was input55 switch ( grade ) { // switch structure nested in while56 57 case 'A': // grade was uppercase A58 case 'a': // or lowercase a59 ++aCount; // increment aCount60 break; // necessary to exit switch61 62 case 'B': // grade was uppercase B63 case 'b': // or lowercase b64 ++bCount; // increment bCount 65 break; // exit switch66 67 case 'C': // grade was uppercase C68 case 'c': // or lowercase c69 ++cCount; // increment cCount 70 break; // exit switch71


4472 case 'D': // grade was uppercase D73 case 'd': // or lowercase d74 ++dCount; // increment dCount 75 break; // exit switch76 77 case 'F': // grade was uppercase F78 case 'f': // or lowercase f79 ++fCount; // increment fCount 80 break; // exit switch81 82 case '\n': // ignore newlines, 83 case '\t': // tabs, 84 case ' ': // and spaces in input85 break; // exit switch86 87 default: // catch all other characters88 cout << "Incorrect letter grade entered."89 << " Enter a new grade." << endl;90 break; // optional; will exit switch anyway91 92 } // end switch93 94 } // end while95 } // end function inputGrades


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96 // display a report based on the grades entered by user97 void GradeBook::displayGradeReport()98 { 99 // output summary of results100 cout << "\n\nTotals for each letter grade are:" 101 << "\nA: " << aCount // display number of A grades102 << "\nB: " << bCount // display number of B grades103 << "\nC: " << cCount // display number of C grades 104 << "\nD: " << dCount // display number of D grades105 << "\nF: " << fCount // display number of F grades106 << endl; 107 } // end function displayGradeBook


461 // figure05_11.cpp2 // Create GRadeBook object, input grades and display grade report3 #include “GradeBook.h” // include definition of class Analysis45 int main()6 {7 GradeBook myGradeBook(“MECH215 Introduction to C++ Programming"); 89 myGradeBook.displayMessage(); // Display Welecome Message 10 myGradeBook.inputGrades(); // read grades from user11 myGradeBook. displayGradeReport(); // Display report based on grades12 return 0; // indicate that program ended successfully 13 } // end main


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break and continue Statements

• break statement– Immediate exit from while, for, do/while, switch

– Program continues with first statement after structure

• Common uses– Escape early from a loop– Skip the remainder of switch


Outline48

1 // Fig. 5.13: fig05_13.cpp2 // Using the break statement in a for structure.3 #include <iostream>4 5 using std::cout;6 using std::endl;7 8 // function main begins program execution9 int main()10 {11 12 int x; // x declared here so it can be used after the loop13 14 // loop 10 times15 for ( x = 1; x <= 10; x++ ) {16 17 // if x is 5, terminate loop18 if ( x == 5 )19 break; // break loop only if x is 520 21 cout << x << " "; // display value of x22 23 } // end for 24 25 cout << "\nBroke out of loop when x became " << x << endl;


Outline49

26 27 return 0; // indicate successful termination28 29 } // end function main

1 2 3 4

Broke out of loop when x became 5


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break and continue Statements

• continue statement– Used in while, for, do/while– Skips remainder of loop body– Proceeds with next iteration of loop

• while and do/while structure– “Loop-continuation test” evaluated immediately

after the continue statement

• for structure– Increment expression executed– Next, loop-continuation test evaluated


Outline51

1 // Fig. 2.27: fig02_27.cpp2 // Using the continue statement in a for structure.3 #include <iostream>4 5 using std::cout;6 using std::endl;7 8 // function main begins program execution9 int main()10 {11 // loop 10 times12 for ( int x = 1; x <= 10; x++ ) {13 14 // if x is 5, continue with next iteration of loop15 if ( x == 5 )16 continue; // skip remaining code in loop body17 18 cout << x << " "; // display value of x19 20 } // end for structure21 22 cout << "\nUsed continue to skip printing the value 5" 23 << endl;24 25 return 0; // indicate successful termination


Outline52

26 27 } // end function main

1 2 3 4 6 7 8 9 10

Used continue to skip printing the value 5


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Logical Operators

• Used as conditions in loops, if statements

• && (logical AND)– true if both conditions are true

if ( gender == 1 && age >= 65 )

++seniorFemales;

• || (logical OR)– true if either of condition is true

if ( semesterAverage >= 90 || finalExam >= 90 ) cout << "Student grade is A" << endl;


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Logical Operators

• ! (logical NOT, logical negation)– Returns true when its condition is false, & vice

versaif ( !( grade == sentinelValue ) ) cout << "The next grade is " << grade << endl;

Alternative:if ( grade != sentinelValue ) cout << "The next grade is " << grade << endl;


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

• Common error– Does not typically cause syntax errors

• Aspects of problem– Expressions that have a value can be used for

decision• Zero = false, nonzero = true

– Assignment statements produce a value (the value to be assigned)


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• Exampleif ( payCode == 4 )

cout << "You get a bonus!" << endl;

– If paycode is 4 bonus given

• If == was replaced with =if ( payCode = 4 ) cout << "You get a bonus!" << endl;

– Paycode set to 4 (no matter what it was before!)– Statement is true (since 4 is non-zero)– Bonus given in every case


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• Lvalues– Expressions that can appear on left side of

equation– Can be changed (i.e., variables)

• x = 4;

• Rvalues– Only appear on right side of equation– Constants, such as numbers (i.e. cannot write 4

= x;)

• Lvalues can be used as rvalues, but not vice versaNOTE: x = 1 and x == 1


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Structured-Programming Summary


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

modify

• Rules for structured programming– Only use single-entry/single-exit control structures– Rules

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

rectangles (actions) in sequence3) 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


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• All programs 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

Documents

2003 Prentice Hall, Inc. All rights reserved. 1 Control Structures Outline Assignment Operators Increment and Decrement Operators Essentials of Counter-Controlled