2006 Pearson Education, Inc. All rights reserved. 1 3 3 Control Statements: Part 1: Selection statements: if, if…else, switch

2006 Pearson Education, Inc. All rights reserved.

1

33Control Statements:

Part 1:Selection statements: if, if…else, switch


2

Control StatementsControl Statements

• Normally, statements in program are executed one after the other in the order in which they’re written.

• This is called sequential execution• Example: calculate area of rectangle.• There are control statements enable you to specify that the next one

in sequence.• This is called transfer of control.• The control statements are categorized in almost two groups: Selection control statements. Repetition control statements.


3

Control StructuresControl Structures

• Sequence structure– Programs executed sequentially by default

• Selection structures– if, if…else, switch

• Repetition structures– while, do…while, for


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Sequential ExecutionSequential Execution

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11

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Fig. 3.1 | Equality and relational operators. Fig. 3.1 | Equality and relational operators.

Standard algebraic equality or relational operator

C++ equality or relational operator

Sample C++ condition

Meaning of C++ condition

Relational operators

> x > y x is greater than y

< x < y x is less than y

>= x >= y x is greater than or equal to y

<= x <= y x is less than or equal to y

Equality operators

= == x == y x is equal to y

≠ != x != y x is not equal to y


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Fig.3.2 | Arithmetic operators. Fig.3.2 | Arithmetic operators.

C++ operation C++ arithmetic operator

Algebraic expression

C++ expression

Addition + f + 7 f + 7

Subtraction - p – c p - c

Multiplication * bm or b· m b * m

Division / x / y or x

y or x ÷ y x / y

Modulus % r mod s r % s


If Selection StatementIf Selection Statement

• Condition– Expression can be either true or false– Can be formed using equality or relational

operators.

• if statement– If condition is true, body of the if statement

executes– If condition is false, body of the if statement

does not execute.

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• Selection statements– Pseudocode example

• If student’s grade is greater than or equal to 60Print “Passed”– If the condition is true

» Print statement executes, program continues to next statement

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



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Relational Expression


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Arithmetic Expression


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OutlineOutline

fig02_13.cpp

(1 of 2)

1 // Fig. 2.13: fig02_13.cpp

2 // Comparing integers using if statements, relational operators

3 // and equality operators.

4 #include <iostream> // allows program to perform input and output

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6 using std::cout; // program uses cout

7 using std::cin; // program uses cin

8 using std::endl; // program uses endl

9

10 // function main begins program execution

11 int main()

12 {

13 int number1; // first integer to compare

14 int number2; // second integer to compare

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16 cout << "Enter two integers to compare: "; // prompt user for data

17 cin >> number1 >> number2; // read two integers from user

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19 if ( number1 == number2 )

20 cout << number1 << " == " << number2 << endl;

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22 if ( number1 != number2 )

23 cout << number1 << " != " << number2 << endl;

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25 if ( number1 < number2 )

26 cout << number1 << " < " << number2 << endl;

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28 if ( number1 > number2 )

29 cout << number1 << " > " << number2 << endl;

30

using declarations eliminate need for std:: prefix

Can write cout and cin without std:: prefix

Declare variables

if statement compares values of number1 and number2 to test for equality

If condition is true (i.e., values are equal), execute this statementif statement compares values

of number1 and number2 to test for inequality

If condition is true (i.e., values are not equal), execute this statement

Compares two numbers using relational operator < and >


18OutlineOutline

fig02_13.cpp

(2 of 2)

fig02_13.cpp output (1 of 3)

(2 of 3)

(3 of 3)

31 if ( number1 <= number2 )

32 cout << number1 << " <= " << number2 << endl;

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34 if ( number1 >= number2 )

35 cout << number1 << " >= " << number2 << endl;

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37 return 0; // indicate that program ended successfully

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39 } // end function main Enter two integers to compare: 3 7 3 != 7 3 < 7 3 <= 7 Enter two integers to compare: 22 12 22 != 12 22 > 12 22 >= 12 Enter two integers to compare: 7 7 7 == 7 7 <= 7 7 >= 7

Compares two numbers using relational operators <= and >=


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Fig. 3.2 | Precedence and associativity of the operators discussed so far. Fig. 3.2 | Precedence and associativity of the operators discussed so far.

Operators Associativity Type

() left to right parentheses

* / % left to right multiplicative

+ - left to right additive

<< >> left to right stream insertion/extraction

< <= > >= left to right relational

== != left to right equality

= right to left assignment


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Fig. 3.3 | C++ keywords.

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

and and_eq asm bitand Bitor bool catch class compl const_cast

delete dynamic_cast explicit export False

friend inline mutable namespace New not not_eq operator or or_eq

private protected public reinterpret_cast static_cast

template this throw true Try typeid typename using virtual wchar_t xor xor_eq


Selection Statements: IF Statements

Example:

Write a program that accept an integer from the user and in case integer is even print out the following message

• “This number is even”

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Answer:22


• Important note:

• If (x==10)

• if (x=10)

• These expressions are not the same.

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Selection Statement: IF Else Statement24


Selection Statement: IF Else Statement25


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If…else Double-Selection Statement

• if– Performs action if condition true

• if…else– Performs one action if condition is true, a different action if it is false

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

print “Passed”Else print “Failed”

• C++ code– if ( grade >= 60 )

cout << "Passed";else cout << "Failed";


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Example: Write a program that accept an integer from the user and print it is Positive or Negative number.


Answer29


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IF…else Double-Selection Statement (Cont.)

• 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


Program of calculating the result of students

#include <iostream>

//#include <conio.h>

using namespace std;

int main()

{

int grade;

cout <<"enter the grade of the student \n";

cin>> grade;

if (grade>=60)

cout <<"Passed\n";

else

cout <<"Failed \n";

getchar();

return 0;

}

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Nested IF32


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Nested If

• Dangling-else problem– Compiler associates else with the immediately

preceding if– Example

• if ( x > 5 ) if ( y > 5 ) cout << "x and y are > 5";else cout << "x is <= 5“;


#include <iostream>

#include <conio.h>


int main()

{

int x, y;

cout<<“Enter any two numbers \n”;

cin>>x>>y;

if ( x > 5 ) if ( y > 5 ) cout << "x and y are > 5";else cout << "x is <= 5“;

getch();

}

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Program of assigning a grade to students

#include <iostream>

#include <conio.h>


int main()

{

int studentGrade ;

cout<<“Enter the marks”;

cin>> studentGrade;

if ( studentGrade >= 90 ) cout << "A";else if (studentGrade >= 80 ) cout << "B";else if (studentGrade >= 70 ) cout << "C"; else if ( studentGrade >= 60 ) cout << "D";else cout << "F";

getch();

}

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#include <iostream>

#include <conio.h>


int main()

{

int x, y;

cout<<“Enter any two numbers \n”;

cin>>x>>y;

if ( x > 5 ){ if ( y > 5 ) cout << "x and y are > 5";}else cout << "x is <= 5";

getch();

}

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3.6 if…else Double-Selection Statement (Cont.)

• Dangling-else problem (Cont.)– Rewrite with braces ({})

• if ( x > 5 ){ if ( y > 5 ) cout << "x and y are > 5";else cout << "x is <= 5";

• }

– Braces indicate that the second if statement is in the body of the first and the else is associated with the first if statement


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3.6 if…else Double-Selection Statement (Cont.)

• Compound statement– Also called a block

• Set of statements within a pair of braces• Used to include multiple statements in an if body

– Example• if ( studentGrade >= 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 executes


#include <iostream>

#include <conio.h>


int main()

{

int grade;

cout<<“Enter grade \n”;

cin>>grade;

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

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If-else if statement

• Also means to write an if statement within another if statement.

– One inside another, test for multiple cases – Once a condition met, other statements are skipped– Example

• 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”


IF- Else IF statement41


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IF- Else IF statement (Cont.)

• Nested if…else statements (Cont.)

– Written In C++• if ( studentGrade >= 90 ) cout << "A";else if (studentGrade >= 80 ) cout << "B"; else if (studentGrade >= 70 ) cout << "C"; else if ( studentGrade >= 60 ) cout << "D"; else cout << "F";


Program of assigning a grade to students

#include <iostream>

#include <conio.h>


int main()

{

int marks;

cout<<“Enter the marks”;

cin>>marks;

if ( marks >= 90 ) cout << "A";else if (marks >= 80 ) cout << "B"; else if (marks >= 70 ) cout << "C"; else if ( marks >= 60 ) cout << "D"; else cout << "F";

getch();

}

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IF- Else IF statement(Cont.)

• Nested if…else statements (Cont.)

– Written In C++ (indented differently)

• if ( studentGrade >= 90 ) cout << "A";else if (studentGrade >= 80 ) cout << "B";else if (studentGrade >= 70 ) cout << "C"; else if ( studentGrade >= 60 ) cout << "D";else cout << "F";


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Logical Operators

• Logical operators– Allows for more complex conditions

• Combines simple conditions into complex conditions

• C++ logical operators– & (logical AND)

– | (logical OR)

– ! (logical NOT)


Logical Operators 46


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Logical Operators (Cont.)

• Logical AND (&) Operator– Consider the following if statement

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

seniorFemales++;

– Combined condition is true • If and only if both simple conditions are true

– Combined condition is false • If either or both of the simple conditions are false

والشرط ) • األول الشرط الجزئين بفحص المترجم يقومالثاني(


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Fig. 3.5| && (logical AND) operator truth table.

expression1 expression2 expression1 && expression2

false false false false true false true false false true true true


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• Logical OR (|) Operator– Consider the following if statement

if ( ( semesterAverage >= 90 ) |( finalExam >= 90 ))

cout << “Student grade is A” << endl;

– Combined condition is true • If either or both of the simple conditions are true

– Combined condition is false • If both of the simple conditions are false


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Fig. 3.6 | || (logical OR) operator truth table.

expression1 expression2 expression1 || expression2

false false false false true true true false true true true true


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• Short-Circuit Evaluation of Complex Conditions– Parts of an expression containing && or || operators are

evaluated only until it is known whether the condition is true or false

– Example• (( gender == 1 ) && ( age >= 65 ))

– Stops immediately if gender is not equal to 1• Since the left-side is false, the entire expression must be false

األول • الجزء بفحص المترجم يقوم الحالة هذه في ) فحص) يتابع صحيحة قيمته كانت إذا األول الشرط

) قيمته ) كانت إذا أما ، الثاني الشرط الثاني الجزء. الثاني الجزء فحص في يواصل فال خطأ


Example54


Example55


What is the output?#include<iostream>


int main()

{

int a=7;

int b=8;

if ((a>10) & (++b>7))

{

cout<<"that is right \n";

cout<<b;

}

return 0;

}

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#include<iostream>


int main()

{

int a=7;

int b=8;

if ((a>10) & (++b>7))


cout<<b;

return 0;

}

No output 9

#include<iostream>


int main()

{

int a=7;

int b=8;

if ((a>10) & (++b>7))


cout<<b;

return 0;

}

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What is the Output?57

#include<iostream>


int main()

{

int x=5;

if (x=4)

cout<<“True \n";

else

cout<<“False \n”;

return 0;

}

#include<iostream>


int main()

{

int x=5;

if (x==4)

cout<<“True \n";

else


return 0;

}

Trueغير القيمة أن بما

صحيح فالشرط صفرالقاعدة حسب

False

#include<iostream>


int main()

{

int x=5;

if (x=0)

cout<<“True \n";

else


return 0;

}

Falseصفر القيمة أن بما

الشرط falseفسيعتبرالقاعدة حسب


What is the output for each program?

#include <iostream>


int main()

{

int x, y;

x=7; y=10;

if ( x > 5 )

{if ( y > x ) cout << "x and y are > 5";

} else cout << "x is <= 5";

}

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#include <iostream>


int main()

{

int x, y;

X=4; y=10;

if ( x > 5 )

{if ( y > x )cout << "x and y are > 5";}else cout << "x is <= 5";

}

#include <iostream>


int main()

{

int x, y;

X=7; y=5

if ( x > 5 )

{if ( y > x )cout << "x and y are > 5";}else cout << "x is <= 5";

}

x and y are > 5 x is <= 5 No output


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• Logical Negation (!) Operator– Unary operator

– Returns true when its operand is false, and vice versa

– Example• if ( !( grade == sentinelValue ) ) cout << "The next grade is " << grade << endl;is equivalent to:if ( grade != sentinelValue ) cout << "The next grade is " << grade << endl;

• Stream manipulator boolalpha– Display bool expressions in words, “true” or “false”


What is output?60

#include<iostream>


int main()

{

int x=5;

if (!(x=4))

cout<<“True \n";

else


return 0;

}

False


PART TWO

SWITCH STATEMENT

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Selection Statements: Switch Statement

The switch control statement that allows us to make a decision from the number of choices.

• Expression: It could be an integer constant like 1,2 or 3, or an expression that evaluates to an integer.

• Constant: is a specific value.

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65



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Wrong:Case >=50Case a+b


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switch Multiple-Selection Statement (Cont.)

• switch statement

– Controlling expression

• Expression in parentheses (أقواس)after keyword switch

– case labels

• Compared with the controlling expression

• Statements following the matching case label are executed

– Braces are not necessary around multiple statements in a case label

– A break statements causes execution to proceed (تمضي)with the first statement after the switch

• Without a break statement, execution will fall through to the next case label


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switch Multiple-Selection Statement

•switch statement– Used for multiple selections

– Tests a variable or expression• Compared against constant integral expressions to decide on

action to take

– Any combination of character constants and integer constants that evaluates to a constant integer value


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switch Multiple-Selection Statement (Cont.)

•switch statement (Cont.)– default case

• Executes if no matching case label is found

• Is optional

– If no match and no default case

• Control simply continues after the switch



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للحرف الرقمية القيمة إختبار يتمعن عبارة ASCII CODEوهي


Selection Statements: Switch Statement71


What is the output#include<iostream>


int main()

{

int i=20;

switch(i+10)

{

case 10:

cout<<"I am in level 1 \n"; break;

case 20:

cout<<"I am in level 2 \n"; break;

case 30:

cout<<"I am in level 3 \n“; break;

default:

cout<<"I am in default \n";

}

return 0;

}

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I am in level 3


What is the output?#include<iostream>


int main()

{

int i=20;

switch(i+10)

{

case 10:

cout<<"I am in level 1 \n"; //break;

case 20:

cout<<"I am in level 2 \n"; //break;

case 30:

cout<<"I am in level 3 \n“; //break;

default:

cout<<"I am in default \n";

}

return 0;

}

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I am in level 1I am in level 2I am in level 3I am in default


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Error in this switch expression 75


Error in case statement76






Can I apply this example for switch?79

NoBecause in this if example we put the condition between range.We can not put < or > in switch. We must put specific value.


Switch and If else

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References

مراجع:

المحاضر محاضرات من أخذها تم شرائح هنالكالدسوقي إبراهيم محمد

Programming Basics For Beginners

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End

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Documents

2006 Pearson Education, Inc. All rights reserved. 1 3 3 Control Statements: Part 1: Selection statements: if, if…else, switch