lecture 19 part 1.pdf

7/27/2019 Lecture 19 Part 1.pdf

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1992-2012 by Pearson Education, Inc. & John Wiley & SonsSome portions are adopted from C++ f or Everyone by Horstmann

ENGR 1200U Introduction to Programming

Lecture 19

Modular Programming with Functions (Chapter 6)

(contd)

Dr. Eyhab Al-Masri

ENGR 1200U

Winter 2013 - UOIT

A program may be broken downinto a set of manageablefunctions, or modules.

Thisiscalled________________________________.

ModularProgramming


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What is a function call?What is a function definition?

Afunctioncallisastatementthatcausesafunctionto

execute.

Afunctiondefinitioncontainsthestatementsthatmakeup

the

functions.

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Winter 2013 - UOIT

When creating a function, you mustcreate its __________ . It consists of

the following parts:

definition:Allfunctiondefinitionshavethefollowingparts:

Name Everyfunctionmusthaveaname

Parameterlist Listofvariablesthatholdthevalues

beingpassedtothefunction.

Body Bodyofthefunction(setofstatements

thatcarryoutthetaskofthefunction

isperforming).Enclosedinbraces.


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Winter 2013 - UOIT

Fill-in the blanks:

double cube_volume(double side_length)

{

double volume=side_length *side_length *side_length;

return volume;

}

return type name parameter list

body

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Winter 2013 - UOIT

What is the output of the following program?

Hellofrommain.

HellofromthefunctiondisplayMessage.

Backinfunctionmainagain.


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What is a function prototype?

Afunctionprototypeeliminatestheneedtoplacea

functiondefinitionbeforeallcallstothefunction.

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When a function is called, theprogram may send values into thefunction. Values that are sent in afunction call are called _________.

arguments

Example:result=pow(2.0,4.0);

A

parameter is

a

special

variable

that

holds

a

value

beingpassedasanargumentintoafunction.

Example:voiddisplayValue(int num)


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Givenaninputof

487

Outputis:

Thesumis19

1//Thisprogramdemonstratesafunctionwiththreeparameters.

2

#include 3using namespace std;4

5//Functionprototype

6void showSum(int num1,int num2,int num3);

7

8int main()

9{

10int value1,value2,value3;

11

12//Get3integers

13coutvalue2>>value3;

16

17//CallshowSum,passing3arguments

18showSum(value1,value2,value3);

19return 0;

20

}21

22void showSum(int num1,int num2,int num3)

23{23 cout


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ProgramOutput

Inmainnumberis12

InchangeMe,thevaluehasbeenchangedto0Backinmainagain,numberisstill12

#include

using namespace std;

void changeMe(int aValue);

int main()

{

int number=12;

cout


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Winter 2013 - UOIT

Can a function send a value back toa part of a program? (contd)

int sum(int num1,int num2)

{

return num1+num2;

}

//assumevalues20and4

0arepassedintosum

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Winter 2013 - UOIT

Can functions return true or falsevalues?

Yes. Sometimes there is a

need for a function that

tests an argument and

returns a true or falsevalue indicating whether or

not a condition is

satisfied.

bool isValid(int number)

{

bool status;

if (number>=1&&number


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Can functions return true or falsevalues? (contd)

This code snippet shows an if/else statement that makes a

call to the function:

int value=20;

if (isValid(value))

cout


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Winter 2013 - UOIT

When the function begins, its parameter variables andany local variables it defines are created in memory

When function ends, these variables are destroyed

This means that any values stored in a functions

parameters or local variables are lost between calls tothe function.

A local variable exists only while the function it isdefined in is executing

This is known as lifetime of a local variable

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Winter 2013 - UOIT

int sum(int num1,int num2)

{

int result=num1+num2;

return result;}

It is possible to use parameter variablesto initialize local variables


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Global constants are typically used to representunchanging values that are needed throughout aprogram

Example: Suppose a banking program uses anamed constant to represent an interest rate. If interest rate is used in several functions, it is easier to

create a global constant, rather than a local namedconstant in each function

A global constant is a named constant that isavailable to every function in a program

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Winter 2013 - UOIT

You cannot have two local variables with thesame name in the same function

This applies to parameter variables as well

A parameter variable, in essence, a local variable.Hence, you cannot give a parameter variable and a localvariable in the same function the same name!

However, you can have a parameter or localvariable with the same name as a global variableor constant


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This is because local variables are destroyedwhen a function terminates

Local variables are also recreated when the

function starts again

If a function is called more than once in aprogram, the values stored in the functions localvariables do not persist between function calls

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This is accomplished by making the variable static Static variables are not destroyed when a function

returns They exist for the entire lifetime of the program, even

though their scope is only the function in which they aredefined

Sometimes it is desirable for a program toremember what value is stored in a localvariable between function calls.


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What is a reference variable?

Areferencevariableisavariablethatreferencesthe

memorylocationofanothervariable

Anychangemadetothereferencevariableisactually

made

to

the

one

it

references

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Winter 2013 - UOIT


ProgramOutput

Inmain,valueis4

NowcallingdoubleNum...

Nowbackinmain,valueis8

//Thisprogramusesareferencevariableasafunctionparameter.

#include


void doubleNum(int &refVar);

int main()

{

int value=4;cout


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New programmers often have difficulty determiningwhen an argument should be passed to a function byreference and when it should be passed by value

Here are some general guidelines: When an argument is a constant, it must be passed by

value

When a variable is passed as an argument should nothave its value changed, it should be passed by value

This protects it from being altered

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Winter 2013 - UOIT

Here are some general guidelines (contd):

When two or more variables passed as arguments to afunction need to have their values changed by thatfunction, they should be passed by reference

When a copy of an argument cannot reasonably orcorrectly be made, such as when the argument is a file

stream object, it must be passed by reference


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Here are three common instances when referenceparameters are used:

When data values being input in a function need to beknown by the calling function

When a function must change existing values in thecalling function

When a file stream object is passed to a function

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Winter 2013 - UOIT

Sometimes you will create two or more functions that perform thesame operation, but use a different set of parameters, orparameters of different data types

Example: Suppose there is a square function that uses a double

parameter

Also, suppose you also wanted a square function that worksexclusively with integers and accepts an int as its argument

Both functions would do the same thing, return the square of theirargument

The only difference is the data type involved in the operation

A Two or more functions may have the same name, aslong as their parameter lists are different


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Example: squareInt, and squareDouble

C++, however, allows you to overload function names

This means you may assign the same name to multiplefunctions, as long as their parameters lists aredifferent

If you were to use both these functions in the same program, youcould assign a unique name to each function

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#include

#include


int square(int);

double square(double);

int main()

{

int userInt;

double userReal;

cout

userInt >>

userReal;cout


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The exit() function causes a program to terminate, regardless ofwhich function or control mechanism is executing

#include

#include //Neededtousetheexitfunctioninsomecompilers


void someFunction();

int main()

{

someFunction();

return 0;

}

void someFunction()

{

cout

lecture 19 part 1.pdf

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