What are Parameters?

Parameters are variables used in programming that allow you to pass data or values into functions, methods, or procedures to enable them to perform tasks with varying inputs. When you define a function or method, you can specify parameters in its declaration, which are placeholders for the values that will be passed when the function is called. Parameters act as input data for the function and allow it to process different values each time it is executed.

Parameters are essential in making functions reusable and dynamic. By defining parameters, functions can perform tasks based on the values passed to them, without having to hard-code specific data. They serve as a critical component of function-based programming and are used in many programming languages such as Python, Java, JavaScript, C, C++, and more.

In many cases, parameters are also referred to as arguments, though there is a subtle distinction between the two:

• Parameter: The variable in the function definition.
• Argument: The actual value passed to the parameter when the function is called.

For example, consider a simple function that adds two numbers:

def add_numbers(a, b):
    return a + b

Here, a and b are parameters. When you call the function with actual values, those values are arguments:

add_numbers(3, 5)

In this case, 3 and 5 are arguments passed to the a and b parameters of the add_numbers function.

What are the Major Use Cases of Parameters?

Parameters are used in a wide range of programming scenarios. Below are the major use cases:

1. Dynamic Function Behavior

Parameters allow functions to behave dynamically by taking input values that determine the function’s behavior. Instead of hardcoding values, parameters allow the same function to be executed with different inputs, making the function reusable for different scenarios.

Example:

• A sum function can be reused for adding any two numbers, and the numbers are passed as parameters to define the function’s behavior.

2. Encapsulation of Complex Operations

Functions that perform complex operations (e.g., calculations, data processing) often require different values for each operation. Parameters encapsulate the input data, allowing the function to work on a variety of inputs without modifying the core logic.

Example:

• A file processing function can take parameters for the file path, encoding, and output format, enabling the same function to process different files.

3. Code Reusability

Parameters increase code reusability by allowing functions to work with different inputs and perform similar operations without writing multiple versions of the same function.

Example:

• A data sorting function can be reused with different datasets and sort orders by passing the dataset and order type as parameters.

4. Configuration of Functions

Parameters allow functions to be configured and customized without changing their internal logic. This allows greater flexibility, as parameters control aspects of the function’s execution, like timeouts, limits, and environment settings.

Example:

• A server connection function might take parameters for the server address, port, and authentication details, allowing the function to connect to various servers with different configurations.

5. Control Flow and Decision Making

Parameters can control the flow of a program, allowing developers to implement decision-making logic within functions based on the input values. This can help in implementing conditional operations and branching logic.

Example:

• A payment processing function could take a payment_method parameter to determine whether the payment is processed via credit card, PayPal, or another method.

6. Interfacing with External Systems

In distributed systems or when working with external APIs, parameters serve as the mechanism to pass data between different services, applications, or system layers. They act as data carriers that transport necessary information across systems.

Example:

• An API request might take parameters like user_id, action_type, and time_range to request specific data from a server.

How Parameters Work Along with Architecture?

In programming, parameters fit into the overall architecture of functions, methods, and procedures. Below is an explanation of how parameters are used within the architecture of a function and the general software architecture.

1. Function Declaration

When you define a function or method, you specify the parameters within the function’s declaration. These parameters act as placeholders for the values that will be passed when the function is invoked.

Example in Python:

def greet_user(username):
    print(f"Hello, {username}!")

Here, username is a parameter that is used in the function greet_user. When you call the function, you pass an argument to this parameter:

greet_user("Alice")

2. Function Call

When a function is invoked, you pass values, known as arguments, to the parameters in the function definition. These arguments replace the parameters with specific data when the function executes. The argument values are assigned to the corresponding parameters, and the function uses them to perform its operations.

3. Parameter Scope

The scope of a parameter is local to the function or method in which it is defined. This means the parameter can only be used inside the function or method where it is declared. Once the function execution is complete, the parameter value is discarded.

Example:

def calculate_area(radius):
    area = 3.14 * radius * radius  # radius is a parameter
    return area

# radius is not accessible outside the function

4. Default Parameters

Some programming languages allow default parameter values, which are used when no argument is passed to the function. This makes parameters optional.

Example in Python:

def greet_user(username="Guest"):
    print(f"Hello, {username}!")

greet_user()  # Uses the default value "Guest"
greet_user("Alice")  # Uses the provided argument "Alice"

5. Varied Number of Parameters (Arbitrary Arguments)

Some languages support functions that accept a variable number of parameters, often using a special syntax. In Python, this is achieved using *args for non-keyword arguments or **kwargs for keyword arguments.

Example in Python:

def sum_numbers(*args):
    return sum(args)

print(sum_numbers(1, 2, 3))  # Output: 6

Here, *args allows the function to accept an arbitrary number of arguments.

Basic Workflow of Parameters

The basic workflow for using parameters in functions follows a few simple steps:

1. Define Parameters in Function Declaration
   • Define the function and specify the parameters inside the parentheses.
2. Call the Function and Pass Arguments
   • When calling the function, pass values (arguments) that correspond to the parameters defined in the function.
3. Use Parameters Inside the Function
   • Inside the function, use the parameter values to perform computations or execute specific tasks based on the input.
4. Return Results (If Applicable)
   • The function can return a value based on the parameters, which can be used elsewhere in the program.
5. Handle Optional or Variable Parameters
   • Define default values for parameters or use variable argument techniques (like *args or **kwargs) to make the function more flexible.

Step-by-Step Getting Started Guide for Parameters

Here’s a step-by-step guide to help you understand and implement parameters in your programs:

Step 1: Define a Simple Function

Start by creating a simple function that accepts a single parameter:

def say_hello(name):
    print(f"Hello, {name}!")

This function takes name as a parameter and prints a greeting.

Step 2: Call the Function with an Argument

Now, call the function and pass an argument to the parameter:

say_hello("Alice")

This will output:

Hello, Alice!

Step 3: Add More Parameters

You can add more parameters to the function to make it more versatile. For example, let’s define a function to calculate the area of a rectangle:

def calculate_area(length, width):
    area = length * width
    return area

Step 4: Call the Function with Multiple Arguments

Pass multiple arguments to the function:

result = calculate_area(5, 3)
print(result)  # Output: 15

Step 5: Use Default Parameters

Let’s add a default value to a parameter. This makes it optional:

def greet_user(username="Guest"):
    print(f"Hello, {username}!")

You can call it with or without an argument:

greet_user()  # Output: Hello, Guest!
greet_user("Bob")  # Output: Hello, Bob!

Step 6: Use Variable-Length Arguments

If you want to accept an arbitrary number of arguments, use *args or **kwargs:

def add_numbers(*args):
    return sum(args)

print(add_numbers(1, 2, 3, 4))  # Output: 10

This allows you to pass any number of arguments to the function.

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The setTimeout() method sets a timer which executes a function or specified piece of code once after the timer expires. The function is only executed once. It returns a positive integer value which identifies the timer created by the call to setTimeout(); this value can be passed to clearTimeout() to cancel the timeout.

Syntax: –
setTimeout (function, milliseconds, para1, para2);
Ex: – var timeoutID = setTimeout(show, 2000);

clearTimeout( ) Method

The clearTimeout() method cancels a timeout previously established by calling setTimeout(). The ID value returned by setTimeout() is used as the parameter for the clearTimeout() method.

Syntax: – clearTimeout (timeoutID);

Ex: – clearTimeout(timeoutID);

setInterval( ) Method

The setInterval() method repeatedly calls a function or executes a code snippet, with a fixed time delay between each call. It returns an interval ID that uniquely identifies the interval, so you can remove it later by calling clearInterval().

Syntax: – setInterval (function, milliseconds, para1, para2);

Ex: – var intervalID = setInterval(show, 2000);

clearInterval( ) Method

The clearInterval() method cancels a timed, repeating action that was previously established by a call to setInterval().

Syntax: – clearInterval (intervalID);

Ex: – clearInterval(intervalID);

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Object instance are created with constructor, which is basically a special function that prepares a new instance of an object for use.

Constructor with Parameter

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When a function returns an object, we call it a factory function. It can produce object instance without new keywords or classes.

Ex:-

Factory Function with Parameter

Ex:-

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Object-oriented programming (OOP) is a programming language model organized around objects rather than “actions” and data rather than logic.

Concepts of OOP

• Encapsulation
• Abstraction
• Inheritance
• Polymorphism

Objects

An object is a collection of properties, and a property is an association between a name (or key) and a value. A property’s value can be a function, in which case the property is known as a method. In addition to objects that are predefined in the browser, you can define your own objects.

Type of Objects

• User-defined Objects – These are custom objects created by the programmer to bring structure and consistency to a particular programming task.

• Native Objects – These are provided by the JavaScript language itself like String, Number, Boolean, Function, Date, Object, Array, Math, RegExp, Error as well as object that allow creation of user-defined objects and composite types.

• Host Objects – These objects are not specified as part of the JavaScript language but that are supported by most host environments, typically browsers like window, navigator.

• Document Objects – These are part of the Document Object Model (DOM), as defined by the W3C. These objects presents present the programmer with a structured interface to HTML and XML documents. Access to the document objects is provided by the browser via the document property of the window object (window.document).

Declaration and initialization of Object

• Using Object Literal

Multiword key required quotation

Declaration and initialization of Object

• Using Object Literal

Declaration and initialization of Object

• Using Object Literal

Declaration and initialization of Object

• Using Object Constructor

Declaration and initialization of Object

• Using Object Constructor

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Arrow Function

• Do not call before definition

• An arrow function cannot contain a line break between its parameters and its arrow.

Arrow Function With Parameter

•With one Parameter
Syntax: (para) => {statement};
Syntax: para => {statement};
•More than one Parameter
Syntax: (para1, para2, paraN) => {statement};
•No Parameter
Syntax: ( ) => {statement};

Arrow Function with Parameter

•Default Parameter
Syntax: (para1, para2 = value) => {statement};
•Rest Parameter
Syntax: (para1, …args) => {statement};

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Syntax: –
function function_name (para1, para2=“value”, para3) // problem undefined
{
Block of statement;
}
Syntax: –
function function_name (para1, para2=“value1”, para3=“value2”)
{
Block of statement;
}

JavaScript also allows the use of arrays and null as default values.

Rest Parameters

The rest parameter allows representing an indefinite number of arguments as an array.

Syntax: –
function function_name (…args)
{
Block of statement;
}

Syntax: –
function function_name (a, …args)
{
Block of statement;
}

The rest operator must be the last parameter to a function.

Rest Vs Arguments

There are three main differences between the rest parameters and the arguments object:-

• Rest parameters are only the ones that haven’t been given a separate name, while the arguments object contains all arguments passed to the function.
• The arguments object is not a real array, while Rest Parameters are Array instances, meaning methods like sort, map, forEach or pop can be applied on it directly.
• The arguments object has additional functionality specific to itself (like the callee property).

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Function are subprograms which are used to compute a value or perform a task.

Type of Function

– Library or Built-in functions

Ex: – valueOf( ) , write( ), alert( ) etc

– User-defined functions

Creating and Calling a Function

Creating a Function

Syntax: –

function function_name( )
{
Block of statement;
}

Calling a Function

Syntax: –
function_name( );

Ex: –
display( );

Rules of Function

• Function name only starts with a letter, an underscore ( _ ).
• Function name cannot start with a number.
• Do not use reserved keywords. e.g. else, if etc.
• Function names are case-sensitive in JavaScript.

How Function Call Works

The code inside a function isn‟t executed until that function is called.

Function with Parameters

Syntax: –
function function_name (parameter1, parameter2, ….)
{
Block of statement;
}

• JavaScript function definitions do not specify data types for parameters.
• JavaScript functions do not perform type checking on the passed arguments.
• JavaScript functions do not check the number of arguments received.

Call Function with Parameter

Syntax: –
function function_name (para1, para2, ….)
{
Block of statement;
}
Syntax:-
function_name(argument1, argument2);

Function Argument Missing

If a function is called with missing arguments, the missing values are set to undefined.

Arguments Object

The arguments object contains an array of the arguments used when the function was called.
This object contains an entry for each argument passed to the function, the first entry’s index starting at 0. The argument’s object is not an Array. It is similar to an Array but does not have any Array properties except length.

Many Function Arguments

If a function is called with too many arguments, these arguments can be reached using the arguments object which is a built-in.

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The information or variables included within the function’s parentheses are referred to as parameters. These are used to keep track of values that can be used during runtime. The comma(,) operator allows the user to input as many arguments as he wants. These options are used to accept inputs during runtime. When transferring numbers, such as during a function call, arguments are used. A parameter is a container for parameters that are given to a function. A value supplied to a function is referred to as an argument. In layman’s terms, both parameter and statement have the same meaning. It’s crucial to keep in mind that each parameter must be accompanied with an argument.

Syntex:-

function function_name($first_parameter, $second_parameter) {
    executable code;
}

Example:-

Setting Default Values for Function parameter:-

In PHP, we may define default arguments for function parameters. If no argument is supplied for a parameter with a default value, PHP will call the function with the parameter’s default specified value.

The default value for the parameter $num in the previous example is 12; if no value is supplied for this parameter in a function call, the default value is used. It’s also required because the option $str has no default value.

Functions with return values:-

Functions can also return values to the portion of the program where they were called. The value is returned to the program section from where it was named using the return keyword. It is possible to return any type of value, including arrays and objects. The return statement also marks the conclusion of the function, stops it from running, and returns the value.

Parameter passing to Functions:-

In PHP, there are two ways to pass an argument to a function.

Pass by Value:– Moving by value changes the value of an argument within a function, while the original value outside the function stays unaffected. This means that a statement that is a duplicate of the original value is transmitted.

Pass by Reference:– As statements are passed via proxy, the original value is transmitted. As a result, the starting value has changed. Using the ampersand symbol in pass by reference, we just transmit the value’s address, where it is kept (&).

Example:-

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A parameter is an entity that stores values. It can be a name, a number or some special characters.

Bash shell provides two kind of parameters.

Positional Parameter and Special Parameter

Bash Positional Parameter – $0, $1, $2 ..

Positional parameters are the arguments given to your scripts when it is invoked. It could be from $1 to $N. When N consists of more than a single digit, it must be enclosed in a braces like ${N}.

The variable $0 is the basename of the program as it was called.

The following example gets two arguments and provides arithmetic operations result between those two integers.

First, create the arithmetic.sh shell script as shown below.

$ cat arithmetic.sh

#!/bin/bash

echo -e “\$1=$1”

echo -e “\$2=$2”

let add=$1+$2

let sub=$1-$2

let mul=$1*$2

let div=$1/$2

echo -e “Addition=$add\nSubtraction=$sub\nMultiplication=$mul\nDivision=$div\n”

Next, execute the arithmetic.sh with proper parameters as shown below.

$ ./arithmetic.sh 12 10

$1=12

$2=10

Addition=22

Subtraction=2

Multiplication=120

Division=1

In the above output $1 has the value 12, and $2 has 10.

Shell built-in ‘let’ allows arithmetic operation to be performed on shell variables. The above script does the arithmetic operations such as addition, subtraction, multiplication and division on the given parameters.

Set / Unset Bash Positional Parameters

The built in set command is used to set and unset the positional parameter.

First, create the positional.sh shell script as shown below.

$ cat positional.sh

#!/bin/bash

# From command line

echo -e “Basename=$0”

echo -e “\$1=$1”

echo -e “\$2=$2”

echo -e “\$3=$3”

# From Set builtin

set First Second Third

echo -e “\$1=$1”

echo -e “\$2=$2”

echo -e “\$3=$3”

# Store positional parameters with -(hyphen)

set – -f -s -t

echo -e “\$1=$1”

echo -e “\$2=$2”

echo -e “\$3=$3”

# Unset positional parameter

set —

echo -e “\$1=$1”

echo -e “\$2=$2”

echo -e “\$3=$3”

The above script prints the command line arguments first, then set command sets the positional parameter explicitly. Set with the – refers end of options, all following arguments are positional parameter even they can begin with ‘-’. Set with ‘–’ without any other arguments unset all the positional parameters.

Next, execute the positional.sh as shown below.

$ ./positional.sh

Basename=positional.sh

$1=12

$2=10

$3=

$1=First

$2=Second

$3=Third

$1=-f

$2=-s

$3=-t

$1=

$2=

$3=

Use Bash $* and $@ to Expand Positional Parameters

This example shows the value available in $* and $@.

First, create the expan.sh as shown below.

$ cat expan.sh

#!/bin/bash

export IFS=’-‘

cnt=1

# Printing the data available in $*

echo “Values of \”\$*\”:”

for arg in “$*”

do

echo “Arg #$cnt= $arg”

let “cnt+=1”

done

cnt=1

# Printing the data available in $@

echo “Values of \”\$@\”:”

for arg in “$@”

do

echo “Arg #$cnt= $arg”

let “cnt+=1”

done

Next, execute the expan.sh as shown below to see how $* and $@ works.

$ ./expan.sh “This is” 2 3

Values of “$*”:

Arg #1= This is-2-3

Values of “$@”:

Arg #1= This is

Arg #2= 2

Arg #3= 3

· The above script exported the value of IFS (Internal Field Separator) with the ‘-’.

· There are three parameter passed to the script expan.sh $1=”This is”,$2=”2″ and $3=”3″.

· When printing the each value of special parameter “$*”, it gives only one value which is the whole positional parameter delimited by IFS.

· Whereas “$@” gives you each parameter as a separate word.

Use $# to Count Positional Parameters

$# is the special parameter in bash which gives you the number of positional parameter in decimal.

First, create the arithmetic.sh as shown below.

$ cat arithmetic.sh

#!/bin/bash

if [ $# -lt 2 ]

then

echo “Usage: $0 arg1 arg2”

exit

fi

echo -e “\$1=$1”

echo -e “\$2=$2”

let add=$1+$2

let sub=$1-$2

let mul=$1*$2

let div=$1/$2

echo -e “Addition=$add\nSubtraction=$sub\nMultiplication=$mul\nDivision=$div\n”

If the number of positional parameters is less than 2, it will throw the usage information as shown below,

$ ./arithemetic.sh 10

Usage: ./arithemetic.sh arg1 arg2

Process related Parameters – $$ and $!

The special parameter $$ will give the process ID of the shell. $! gives you the process id of the most recently executed background process.

The following script prints the process id of the shell and last execute background process ID.

$ cat proc.sh

#!/bin/bash

echo -e “Process ID=$$”

sleep 1000 &

echo -e “Background Process ID=$!”

Now, execute the above script, and check the process id which its printing.

$ ./proc.sh

Process ID=9502

Background Process ID=9503

$ ps

PID TTY TIME CMD

5970 pts/1 00:00:00 bash

9503 pts/1 00:00:00 sleep

9504 pts/1 00:00:00 ps

$

Other Bash Special Parameters – $?, $-, $_

· $? Gives the exit status of the most recently executed command.

· $- Options set using set builtin command

· $_ Gives the last argument to the previous command. At the shell startup, it gives the absolute filename of the shell script being executed.

$ cat others.sh

#!/bin/bash

echo -e “$_”; ## Absolute name of the file which is being executed

/usr/local/bin/dbhome # execute the command.

#check the exit status of dbhome

if [ “$?” -ne “0” ]; then

echo “Sorry, Command execution failed !”

fi

echo -e “$-“; #Set options – hB

echo -e $_ # Last argument of the previous command.

In the above script, the last echo statement “echo -e $_” ($ underscore) also prints hB which is the value of last argument of the previous command. So $_ will give the value after expansion

$ ./others.sh

./others.sh

/home/oracle

Sorry, Command execution failed !

hB

hB

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