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The flow of control refers to the order in which a program’s statements are executed. Unless directed otherwise, the normal flow of control for all programs is sequential. This means that statements are executed in sequence, one after another, in the order in which they are placed within the program. Selection, repetition and function invocation structures permit the flow of control to be altered in defined ways. This chapter introduces to you C++’s selection statements. Repetition and invocation techniques are presented in the next two chapters.

Selection criteria

Relational operators

Relational operators are used to compare two operands for equality and to determine if one numeric value is greater than another. A Boolean value of true or false is returned after two operands are compared. The list of relational operators is given below.

Relational operators


a = = b

(a*b) != c

s == ‘y’

x<= 4

The value of a relational expression such as a>40 depends on the value stored in the variable a.

Logical operators

Logical operators, AND, OR and NOT are used for creating more complex conditions. Like relational operators, a Boolean value of true or false is returned after the logical operation is executed.

When the AND operator,&&, is used with two simple expressions, the condition is true only if both individual expressions are true by themselves.

The logical OR operator, ||, is also applied with two expressions. When using the OR operator, the condition is satisfied if either one or both of the two expressions are true.

The NOT operator,!, is used to change an expression to its opposite state; thus, if the expression has any nonzero value (true),! expression produces a zero value (false). If an expression is false,! expression is true (and evaluates to false).



(age>40) || (term<10)


( i==j) || (a<b) || complete

The relational and logical operators have a hierarchy of execution similar to the arithmetic operators. The following table lists the precedence of these operators in relation to the other operators we have used.

Associativity of operators

Example: Assume the following declarations:

char key = ‘m’;

int i = 5, j = 7, k = 12;

double x = 22.5;

Results of expressions
By evaluating the expressions within parentheses first, the following compound condition is evaluated as:

Evaluation process

The bool data type

As specified by the ANSO/ISO standard, C++ has a built-in Boolean data type, bool, containing the two values true and false. As currently implemented, the actual values represented by the bool values, true and false, are the integer values 1 and 0, respectively. For example, consider the following program, which declares two Boolean variables:



int main()


bool t1, t2;

t1 = true;

t2 = false;

cout<<“The value of t1 is “<<t1

<<“\n and the value of t2 is “<<t2<<endl;

return 0;


The output of the program is:

The value of t1 is 1

and the value of t2 is 0

The if-else statement

The if-else statement directs the computer to select a sequence of one or more statements based on the result of a comparison.

Questions & Answers

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
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Source:  OpenStax, Programming fundamentals in c++. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10788/1.1
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