2003 prentice hall, inc. all rights reserved. 1 sequential execution –statements executed in order...

2003 Prentice Hall, Inc. All rights reserved.

1

• Sequential execution– Statements executed in order

• Transfer of control– Next statement executed not next one in sequence

• 3 control structures (Bohm and Jacopini)– Sequence structure

• Programs executed sequentially by default

– Selection structures• if, if/else, switch

– Repetition structures• while, do/while, for

Chapter 2 - Control Structures


2

Problem : Compute and print the summation of two numbers.

#include <iostream.h>void main() {

int a, b, s;cout<<"Please Enter two numbers:";cin>>a>>b;s = a + b;cout<<"s="<<s<<endl;

}

2.1 Sequential programs


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Problem : Compute the area of the circle. Where area = R2 π


const double Pi = 3.14;int r;cout<<"\n Please enter r";cin>>r;double a;a = Pi * r * r;cout<<"\n Circle's Area =

"<<a<<endl; }


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• C++ keywords– Cannot be used as identifiers or variable namesC++ 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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2.2 if Selection Structure

• Selection structure– Choose among alternative courses of action

– If the condition is true• Print statement executed, program continues to next statement

– If the condition is false• Print statement ignored, program continues

– Indenting makes programs easier to read• C++ ignores whitespace characters (tabs, spaces, etc.)


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2.2 if Selection Structure

• Translation into C++If student’s grade is greater than or equal to 60

Print “Passed”

if ( grade >= 60 ) cout << "Passed";

• if structure – Single-entry/single-exit


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2.3 if/else Selection Structure

• if– Performs action if condition true

• if/else– Different actions if conditions true or false

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


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

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

Condition Value if true Value if false


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• Example

if ( grade >= 90 ) // 90 and above cout << "A";else if ( grade >= 80 ) // 80-89 cout << "B";else if ( grade >= 70 ) // 70-79 cout << "C"; else if ( grade >= 60 ) // 60-69 cout << "D";else // less than 60 cout << "F";

2.3 if/else Selection Structure Nested if/else structures


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• Compound statement– Set of statements within a pair of braces if ( grade >= 60 )

cout << "Passed.\n";else { cout << "Failed.\n"; cout << "You must take this course again.\n";}

– Without braces,cout << "You must take this course again.\n";

always executed

• Block– Set of statements within braces


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Another example

if ( x>y)

{if ( x<z)

cout<<“ Hello”;}

else

cout<<“Hi”;


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2.4 while Repetition Structure

• Repetition structure– Action repeated while some condition remains true– while loop repeated until condition becomes false

• Exampleint product = 2;

while ( product <= 1000 )

product = 2 * product;


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

• Definite repetition– Number of repetitions 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.

2003 Prentice Hall, Inc.All rights reserved.

Outline14

fig02_07.cpp(1 of 2)

1 // Fig. 2.7: fig02_07.cpp2 // Class average program with counter-controlled repetition.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 total; // sum of grades input by user13 int gradeCounter; // number of grade to be entered next14 int grade; // grade value15 int average; // average of grades16 17 // initialization phase18 total = 0; // initialize total19 gradeCounter = 1; // initialize loop counter20


Outline15


fig02_07.cppoutput (1 of 1)

21 // processing phase22 while ( gradeCounter <= 10 ) { // loop 10 times23 cout << "Enter grade: "; // prompt for input24 cin >> grade; // read grade from user25 total = total + grade; // add grade to total26 gradeCounter = gradeCounter + 1; // increment counter27 }28 29 // termination phase30 average = total / 10; // integer division31 32 // display result33 cout << "Class average is " << average << endl; 34 35 return 0; // indicate program ended successfully36 37 } // end function main

Enter grade: 98

Enter grade: 76

Enter grade: 71

Enter grade: 87

Enter grade: 83

Enter grade: 90

Enter grade: 57

Enter grade: 79

Enter grade: 82

Enter grade: 94

Class average is 81

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


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2.5 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)


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2.5 Increment 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.


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

• Same as c += 1

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


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• Preincrement– Variable changed before used in expression

• Operator before variable (++c or --c)

• Postincrement– Incremented changed after expression

• Operator after variable (c++, c--)


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• If c = 5, then – cout << ++c;

• c is changed to 6, then printed out

– cout << c++; • Prints out 5 (cout is executed before the increment. • c then becomes 6


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• When variable not in expression– Preincrementing and postincrementing have same effect

++c;

cout << c;

and c++;

cout << c;

are the same


Outline22


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


Outline23



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

5

5

6

5

6

6


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2.6 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


Outline25


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


Outline26


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Problem : Print the following numbers.1 3 5 7 9 11


int i=1;while (i <= 11) {

cout<<i<<'\t';i+=2; }

}

Remark:Write ((i+=2) <= 11 ) condition instead of the above one. What changes you have to do to produce the same output.


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Problem : Read five numbers from the user and print the positive numbers only.


int num, j=0;while ( j++ < 5 ) {

cout<<"Enter the next num:";cin>>num;if (num > 0)

cout<<num<<endl; }}


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Problem : Compute and Print the value of M where M = 2 * 4 * 6 * … * n


int N, M=1, i=2;cout<<"Enter the upper limit:";cin>>N;while ( i <= N ) {

M *= i;i += 2; }

cout<<"\nM="<<M;}


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2.6 Essentials 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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2.7 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

No semicolon after last statement


Outline32


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


Outline33


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Problem : Print the following numbers.1 3 5 7 9 11

#include <iostream.h>void main( ) {

for (int k=1; k<=11; k+=2) cout<<k<<“\t”;

cout<<endl;}


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Problem : Print the following numbers.20 17 14 11 8 5 2


for (int m=20; m>=2; m-=3) cout<<m<<“\t”;

cout<<endl;}


36

Problem : Compute and print the summation of any 10 numbers entered by the user.


int S=0, N;for (int i=10; i>=1; i--) {

cout<<"\nPlease Enter the next number:";cin>>N;S+=N;}

cout<<"\nS="<<S<<endl;}


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Problem : Compute and Print the factorial of the number 5. (Fact = 5 * 4 * 3 * 2 * 1)


int Fact=1;for (int j=5; j>=1; j--)

Fact *= j;cout<<"5!= "<<Fact<<endl;

}


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• Note: 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;


39

2.8 switch Multiple-Selection Structure

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

statements break;

}


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2.8 switch Multiple-Selection Structure


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Switch(grade)

{case ‘A’: cout<<“The Grade is A”;

break;

case ‘B’: cout<<“The Grade is B”;

break;

case ‘C’: cout<<“The Grade is C”;

break;

case ‘D’: cout<<“The Grade is D”;

break;

case ‘F’: cout<<“The Grade is F”;

break;

Default: cout<< “The Grade is invalid”;

}

switch examples


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#include<iostream.h>int main(){ int a; cout<<“ Enter an Integer between 0 and 10: “; cin>>a; cout<<“\nThe number you entered is “<<a<<endl; switch(a) { case 0: case 1: cout<<“hello”; case 2: cout<<“there”; case 3: cout<<“I am”; case 4: cout<<“Mickey”<<endl; break; case 5: cout<<“How “; case 6: case 7: case 8: cout<<“are you “<<endl; break; case 9: break; case 10: cout<<“Have a nice day. “<<endl; break; default: cout<<“sorry, the number is out of range.”<<endl; }cout<< “ out of switch structure.”<<endl;return 0;

}//main

switch examples


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Switch(score/10)

{

case 0: case 1: case 2:

case 3: case 4: case 5: grade = ‘F’;

break;

case 6: grade = ‘D’;

break;

case 7: grade = ‘C’;

break;

case 8: grade = ‘B’;

break;

case 9: case 10: grade = ‘A’;

break;

default: cout<<“Invalid test score.”<<endl;

}

switch examples


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Switch (age>=18)

{

case 1: cout<<“old enough to be drafted.”<<endl;

cout<< “old enough to vote.”<<endl;

break;

case 0: cout<<“Not old enough to be drafted.”<<endl;

cout<< “Not old enough to vote.”<<endl;

}

switch examples


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2.9 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 );


Outline46



1 // Fig. 2.24: fig02_24.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

1 2 3 4 5 6 7 8 9 10

Notice the preincrement in loop-continuation test.


47

2.10break 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. 2.26: fig02_26.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;

Exits for structure when break executed.


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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2.10break 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

Skips to next iteration of the loop.


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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2.11Logical Operators

• Used as conditions in loops, if statements• && (logical AND)

– true if both conditions are trueif ( 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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2.11Logical Operators

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

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

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


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2.12Confusing 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 versa


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2.13 Operator Precedence

Operator Description Precedence

( ) parentheses Highest

+, – , ! unary plus, unary minus, Not

*, /, %

+ , - Binary plus, binary minus

<, <=, >, >=

== , != Equal, not equal

&&

||

= Assignment Lowest


59

• Find the value of the following expression:(1) 5 + 8 * 2 / 4 16

4

9 (This is the final result)



60

Find value of the following expression

( 9 + 3 ) - 6 / 3 + 5

12

2

10`

15 (this is the final result)



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Find the value of the following Expression

If x = True, y = False, z = False, find the value of the expression x && y || z

x && y || z

False

False (the final result)



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• X=true, Y=false, Z= true

X || Y && Z

true

• X=true, Y=false, Z= false

X || Y && Z

true



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If a = 3, b = 5, x = true, y = false, find the value of the expression: ( a < b ) AND y OR x

( a < b ) && y || x

True

False

True (the final result)

Find the value of the following Expression2.13 Operator Precedence


64

What is the output of the following code:#include <iostream.h>void main() {

int a=10, b=3;cout<<"\n a+b= \t"<<a+b;cout<<"\n a+b*2= \t"<<a+b*2;cout<<"\n (a+b)*2 \t"<<(a+b)*2<<endl;cout<<a<<“<“<<b<<" is\t"<<(a<b);cout<<"\n a+b != a+3 is \t"<<(a+b != a+3);cout<<"\n a+b >= b*2 || a>b+9 is \t"<<(a+b >= b*2 ||

a>b+9)<<endl; }



65

Print the following shape*************************cin>>n;for(int i=1;i<=n;i++) { for (int j=1;j<=n;j++) cout<<“*”; cout<<endl; }

Nested for

2.14 Nested Loops


66

Problem : Draw the following shape***************


for (int raw=1; raw<=5; raw++) {for (int C=1; C<=raw; C++)

cout<<'*';cout<<endl; }

}

Nested for


67

Problem : display the multiplication table for the numbers from 1 to 5.

1 2 3 4 5

2 4 6 8 10

3 6 9 12 15

4 8 12 16 20

5 10 15 20 25

Nested for


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for (int i=1;i<=5;i++)

{

for(int j=1;j<=5;j++)

cout<<i*j<<“\t”;

cout<<endl;

}

Nested for


69

S=m0 + m1 + … +mn

#include <iostream.h>void main(){int s=0,n,m;int t=1;cout<<"Enter m please ";cin>>m;

cout<<"Enter n please ";cin>>n;for (int i=0;i<=n;i++){ t=1; for (int j=1;j<=i;j++)

t=t*m;s=s+t;}cout<<s<<endl;

}

Nested for


70

Problem : Draw the following shape***************


int i=1;while (i<=5) {

int j=1;while (j<=i)

{cout<<'*';j++;}

cout<<endl;i++; }

}

Nested While

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