Lecture 2

Control Structure

Relational Operators

-- From the previous lecture

Relational Operator Meaning

== is equal to

< is less than

> is greater than

<= is less than or equal to

>= is greater than or equal to

!= is not equal to

Logical Operators (&&, ||, !)

• Used for more complex conditions than the other operators

• Helps combine multiple conditions– Logical AND – Condition1 && Condition2– Logical OR – Condition1 || Condition2

• Logical Negation – to reverse condition– if (!(grade == “A”))

• Can be replaced with relational op (!=)– if (grade != “A”)

1

Control Structures

Control Structures• Selection Structures• Looping Structures

Control Structures

• Algorithms – Procedure for solving a problem in terms of

• The actions to be executed

• The order in which actions are to be executed

• Pseudocode– Artificial and informal language that helps

programmers develop algorithms

• Flowchart– Graphical representation of an algorithm

Control Structures• Sequential Execution

– Statements executed one after the other in order in which they are written

Add grade to total

Add 1 to counter

total = total + grade;counter = counter + 1;

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Control Structures

• Selection Structures– Used to choose among alternative courses of action

– if selection structure• Single selection structure

– if /else selection structure• Double selection structure

– switch selection structure• Multiple selection structure

4

Control Structures

• Repetition Structures– Used to repeat an action while a condition

remains true

– for repetition structure– while repetition structure– do/while repetition structure

5

Selection Structures

• if selection structure– Performs an indicated action when the

condition is true.

“Passed”grade >= 60true

false

if (grade >= 60)cout<<“Passed”;

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Statement 1

expression Statement 2

Statement 3

true

false

Selection Structures

• if/else selection structure– Performs an action when the condition is true and

another when the condition is false.

if (grade >= 60)printf (“Passed”);

elseprintf (“Failed”);

print “Passed”grade >= 60truefalse

print “Failed”

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Form and Syntax

If (<Expression>)

<statement>

else

<statement>

int main()

{

int num, neg ,pos;

cout<<“Please enter the no.”;

cin>> num;

if (num < 0)

neg= neg +1;

else

pos= pos +1;

}

Conditional Operator

• Closely related to if/else structure• ?: (Conditional Operator)• Only ternary operator in C

– Takes three operands

• Operands with conditional operator form conditional expression– Operand 1– condition– Operand 2 – action if condition true– Operand 3 – action if condition false

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Conditional Operator

print “Passed”grade >= 60truefalse

print “Failed”

grade >= 60 ? “Passed”: “Failed”

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if (Expression1 )

Statement1

else if (Expression2 )

Statement2...

else if (ExpressionN )

StatementN

else

Statement N+1

EXACTLY 1 of these statements will be executed.

Nested if statements

Nested if/else//nested if/else//printing grades of students

if (grade >= 90)cout<<“A”;

elseif (grade >= 80)

cout<<“B”;else

if (grade >= 70)cout<<“C”;

elseif (grade >= 60)

cout<<“D”;else

cout<<“Failed”;

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Nested if/else

//nested if/else//printing grades of

students

if (grade >= 90)cout<<“A”;

else if (grade >= 80)cout<<“B”;

else if (grade >= 70)cout<<“C”;

else if (grade >= 60)cout<<“D”;

elsecout<<“Failed”;

If grade of a student is 84, the conditionsfor “B”, “C” and “D”are all true. What will be printed?

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Selection Structures

• switch selection structure– Multiple selection structure is useful when

an algorithm contains a series of decisions – Variable or expression is tested separately

for one of several possible values– Each value represents a different action

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Switch Selection Structure

// counting grades assignedint aCount, bCount, cCount, dCount,

fCount;switch (grade){

case ‘A’: case ‘a’:++aCount;

case ‘B’: case ‘b’:++bCount;

case ‘C’: case ‘c’:++cCount;

case ‘D’: case ‘d’:++dCount;

default:++fCount;

}

If grade has value ‘A’, which variable is incremented?

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switch Selection Structure// counting grades assignedint aCount, bCount, cCount, dCount, fCount;switch (grade){

case ‘A’: case ‘a’:++aCount;break;

case ‘B’: case ‘b’:++bCount;break;

case ‘C’: case ‘c’:++cCount;break;

case ‘D’: case ‘d’:++dCount;break;

default:++fCount;

} 14

break Statement

• break statement causes program control to move to the first statement after the selection/ repetition structure

• Switch cases would otherwise run together

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switch Selection Structure

case a actioncase atrue

false

break

case b actioncase btrue

break

default action

false

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Summary of precedence order (revised)

Operator Associativity() left to right

++ -- ! right to left * / % left to right + - left to right< <= > >= left to right == != left to right && left to right || left to right ?: left to right

= += -= *= /= %= right to left, left to right

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Control Structures

• 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