c++ function part 1

8/6/2019 C++ Function Part 1

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BITG 1113:

Function

(Part 1)

LECTURE 6


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Objectives

Prototype and function declaration

The function call and returning value

Local and global variables

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Types of Function

Predefined Function

User-defined Function

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Predefined Function

` Its programming code is already written.

` A programmer only need to know how to use it.

`Need to include the header file in the program

exp : #include

` Some of the predefined mathematical functions in

header file cmath are:

` The power function, pow(x,y)

` Thesquare root function, sqrt(x)

` The floor function, floor(x)

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User-Defined Function

The name of function is used in three ways : fordeclaration, in a call, and for definition.

Function declaration is done first with a prototype

declaration.

Function definition contains the code to completethe task.

Function is invoked or called by Functioncall.

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Declaring, calling and defining functions

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Function Definition

Contains the code for a function.

Two parts : thefunction header and thefunction body

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Function Header

Consist of : the return type, the function name and formalparameter list

Return type

The type of value that will return by the function, the type

of the expression in the return statement must match thereturn type in the function header. For example void, int,

char and double.

Formal Parameter List

List that defines and declares the variables that will

contained the data received by the function

Each variables must be defined and declared fully with

multiple parameters separated by commas.


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9

Function Body

Contains the declarations and statements for the function

Start with local definitions that specify the variables required by

the function.

The functions statement, terminating with a return statement are

coded after local definitions.


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10

Function local variables


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Prototype declaration Consist of three parts : the return part, function name,

and the formal parameter list(has to be same as in functionheader).

Terminated with semicolon.

Placed in global area of the program

General format:

Type Function_name(parameter_list);

Example :

double average (int x, int y);

double average (int, int);

void display ( );

char pilihan ( );


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12

The Function Call

The operand in a function call is the function name.

The operator is the parentheses set,(), which contains the actual

parameters.

Examples of the function calls :

cout


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13More examples of function calls


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Parts of a function call

The Function Call


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15Calling a void function with no parameters

Void functions with no parameters


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Void functions with parameters


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17Pass by Value

Functions that return value


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Programming Example

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int max(int num1, int num2){

int result;

if (num1 > num2)result = num1;

elseresult = num2;

return result;}

return value type method name formal parameters

return value

functionbody

function

header

parameter list

Define a function Invoke a funciton

int z = max(x, y);

actual parameters(arguments)


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int main(){

int i = 5;

int j = 2;int k = max(i, j);

cout


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Trace Function Invocation

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int main()

{

int i = 5;

int j = 2;

int k = max(i, j);

cout


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int main(){

int i = 5;int j = 2;int k = max(i, j);

cout


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int main()

{

int i = 5;

int j = 2;

int k = max(i, j);

cout


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int main(){


cout


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int main()

{

int i = 5;

int j = 2;

int k = max(i, j);

cout


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int main()

{

int i = 5;

int j = 2;

int k = max(i, j);

cout


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int main()

{

int i = 5;

int j = 2;

int k = max(i, j);

cout


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int main(){


cout


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int main()

{

int i = 5;

int j = 2;

int k = max(i, j);

cout


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29

int main(){


cout


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Variable ScopeScope-determines the the part of program in which you can use

defined object.

Global scope any object defined in the global area of the

program is visible from its definition until the end of the

program.

-global variables : variables that are declared outside the function,recognised by any function or program that start after its declaration

Local scope variable defined within a block, visible only in

the block in which they are declares.

- local variables :variables that are declared in the function body and

can only be used in that particular function.

- do not relate to any variable in other function (can have the same name

as variables in other functions)


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31Scope for global and block areas


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Local Variables

You can declare a local variable with the

same name multiple times in different non-

nesting blocks in a function, but you cannot

declare a local variable twice in nested

blocks.

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Local VariablesA variable declared in the initial action part of a for loop

header has itsscope in theentire loop. But a variabledeclared inside a for loop body has itsscope limited in theloop body from its declaration and to theend of theblockthat contains the variable.

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void method1() {

.

.

for (int i = 1; i < 10; i++)

{

.

int j;

.

.

.

}

}

The scope of j

The scope of i


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Local Variables

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voidfunction1()

{

int x = 1;

int y = 1;

for (int i = 1; i < 10; i++)

{

x += i;

}

for (int i = 1; i < 10; i++)

{

y += i;

}}

It is fine to declare i in two

non-nesting blocks

voidfunction2()

{

int i = 1;

int sum = 0;

for (int i = 1; i < 10; i++)

{

sum += i;

}

cout


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#include

using namespace std;

int y;

void t1();

void t2();

int main()

{

t1();

t2();

return 0;

}

void t1()

{int x = 1;

cout


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Unary Scope Resolution

If a local variable name is thesame as a global variable name,you can access the global variable using ::globalVariable. The ::operator is known as theunary scope resolution. For example,the following code:

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#include using namespace std;

int v1 = 10;

int main()

{

int v1 = 5;

cout


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When static is used

#include

using namespace std;

void t1();

int main()

{

t1();

t1();

return 0;

}

void t1()

{

static int x = 1;

int y = 1;

x++;

y++;cout


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THANK YOU

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c++ function part 1

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