Features of a programming language

Features of a programming language

There are many tasks that can be achieved with programming language; most have built in core features that allow programmers to create bigger and better programs. Some of the features that are included in programming languages are:

·         Sequence

·         Selection

·         Iteration

·         Variables

Sequence

A sequence tends to be standard program statements that are executed one after then other this will run in the sequence and will not differentiate the order. As python reads the program in will read it in the order in which it is written this will ensure the program loads step by step.

Selection

Selection statements are in essence what they say to do; they give the user a choice or a selection of answers so they can produce their own outcome. This best example of this would be a very basic calculator; in this instance you ask the user for two numbers, you then ask the user to make a selection from the pre-programmed selections, the code below shows this in a bit more detail.

‘ menu = "Welcome to the Python Calculator\n\ #Store menu text in a string

What calculation would you like to perform?\n\

1. Add\n\

2. Subtract \n\

3. Multiply \n\

4. Divide \n\

5. Square first number \n\

6. Square second number \n\

7. Calculate the power\n"

num1 = int(input("Enter the first number: ")) #important to cast as int

num2 = int(input("Enter the second number: "))

print(menu)

choice = int(input("Enter your choice: ")) #get user choice

if choice == 1:

print(num1 + num2)

elif choice == 2:

print(num1 - num2)

elif choice == 3:

print(num1 * num2)

elif choice == 4:

print(num1 / num2)

elif choice == 5:

print(num1**2)

elif choice == 6:

print(num2**2)

elif choice == 7:

print(num1**num2) ’

Iteration

Another word for iteration could be a loop; there are two types of loops that can be used to repeat certain sections of a programmer’s code. A fixed look would be continuously executed and would only be able to stop if there was an option to use “break;” within the code otherwise the program could continue to run until manually terminated. The other type of loop that can be used are conditional loops these loops will run until a condition has been met this could be either before or maybe ever after the loop has completed at least once.

Pre-Check Loops

A pre-check loop would have the condition placed at the beginning of the loop this would check that the condition is true before the code or loop is executed, if the condition equals false straight from the beginning this would cause the loop not to execute event once. In addition to this if the execution of the loop causes the condition to change it will again have broken the loop and will no longer run. An example of this is shown below:

for loopCounter in range(2,41,2):

    print(loopCounter)

The above snippet of code tells the computer to print all numbers in starting from 2 and ending in 41, the third digit tells the program to only print every second number hence the program counts up in twos like the two times table. The code above will result in the following output:

Post-Check Loops

These types of conditional loops check the condition at the end of the loop this means that the loop will always run at least once to see what the condition is that needs to be met, this would then determine whether or not the program should loop around again, with this being automatically looped there are risks that the program may go into an infinite loop.

height = int(input("Please enter your height (In Inches): "))

while height > 0:

    if height <= 48:

        print("You are the correct height for this ride")

    else:

        print("You are too big for this ride, Sorry!")

               

    height = int(input("Please enter your height: "))

The code above will ask the user their height in inches this will then allow the user to enter their height, and will tell them whether they are able to or are too big to ride the ride. The following screenshot is the result of the code:

Variable

A variable within a program can be classes as many things, for example both inputs and outputs will be stored as variables even if the variable gets changed at a later date. It is stored within the program for a certain period of time depending on which type of variable it is.

The data that can be stored within the variables are made up of numbers and words, when a programmer is coding a program they will have to declare which variable they should use  and the developer should also name the variable in relation to its value.

For example when dealing with numbers an “int” should be used this stands for integer and is a whole number. A string should be used declare words and writing, numbers can be put in this but just as a character and not to be able to do mathematical equations.

Local and Global Variables

Programs are usually made up from a collection of functions. A variable can be declared within a function and it can only be called upon in that function. On the other hand there are global variables these need to be declared at the top of the program this way they are able to be recalled all throughout the program and will save a developer from having to repeat them over and over again.

Input and Output

The input allows the user to interact with the program and input information to provide a different result. An output is the result after the user is has input the information and executed the program both of these will be shown in the screenshot below.

Logical Operators

A logical operator is used when an output or action is dependent on one to several conditions being met. The three operands that are to be used are the following:

·         OR

·         AND

·         NOT

This will only be able to be used to tell the user if the statement is true or false , this will then determine which path the program would then have to go down.

OR = ||

The program would choose a response if either on OR the other condition meets the correct criteria, if neither of them meet the criteria then the program would return false and thus sending the program down the false path. If one of the conditions are true then it would send the program down the true path.

AND &&

The program would again choose a response  but only if both of the conditions are met, for example if both of the conditions are met then the outcome would be true and it would send it on that pathway whereas even if one condition is true but the other is not then the overall outcome would be false and will send it down the false pathway.

NOT !=

This would execute a command or return a value when the condition is false.

Selection Operators

Selection operators tend to be used when if statements are used, when something is dependent on a statement. Depending on the answer will depend on how the program continues, for example:

The selection operator is “<” in this instance is means that if the answer is less than two it will select the first option whereas if the answer is above two it would then select the “else” option. The selection operators are show below:

Operator	Symbol	Purpose
Greater Than	>	This would check to sell if the value on the left was bigger than the value on the right.
Less Than	<	This checks to see that the value on the left is less than the value on the right.
Equal To	==	Checks to see if the two values are equal, if they are the condition would be true.
Greater Than Or Equal To	>=	Checks to see if the value on the left is equal to or greater than the value on the right.
Less Than Or Equal To	<=	Checks to see if the value on the left is equal to or less than the value on the right.
Not equal to	!=	Checks if the value is equal of not if they aren’t then the condition is true.

List / Array

A list or array is a variable with multiple of the same elements stored within is this allows a developer to add delete and recall the list throughout the program whenever they like, it also makes the code more light weight and will ensure the developer doesn’t have to declare every variable every time then want to recall them all instead they will only have to recall the one list variable.

Reading and Writing to and from a text file

Reading and writing allows a user to write and receive information to a text file, a program will need to have the ability to write to a file this allows the program to save and store variables for a later recall.  This will allow for tasks such as creating a log in to recall information from a username and would be able to compare the password to ensure the user is able to log on.

The code below will open a specified text file, anything that has been specified will then be written to the text file it will then be saved.