0.2 - Programming Basics

Tasks

Programming Tasks

• task1
• task2
• task3
• task4

End of Chapter Tasks

• EOC tasks
• Research tasks

Data Types

Notes:

1. In Python 2, the max value for int = 263-1 and min = -263 because Python switches seamlessly from 32 bits to 64 bits once the 32 bit limit is exceeded. In Python 3, it is unbounded.
2. Although float is usually used to refer to single-precision floating point numbers and double is used to refer to double-precision, Python internally uses a C double to represent floats.
3. Limits may vary in different programming languages.
4. Full technical name: Double-precision 64 bit floating point number IEEE 754
5. Void is not used in the same way as None or undefined, although None or undefined may be used a similar way to void.
6. Not strictly built-in but can be accessed through the standard library.
7. Additional types such as linked lists, etc may be available in the languages’ standard library.
8. Python dictionaries are unordered.
9. Other similar implementations exist, which may have slightly different use cases.

Extra Info:

• In Python, characters are represented with strings of length 1. To get the char code of such a string, the oct() method can be used.
• Limits given are theoretical and may slightly differ depending on programming languages and implementations. Practical limits may be a lot lower, e.g: C# objects cannot be over 2GB in memory.
• String limits depend on the encoding used. Using Unicode would mean half the given length is possible.
• Double vs Decimal
  • Less memory
  • Faster floating-point math operations natively supported by processors
  • Larger rane
  • Less accurate compared to Decimal at base 10 numbers.

Keywords

Naming Conventions

How to make your code look a little less painful: agreeing that everyone names everything with generally the same pattern :)

Of course, different companies, institutions, etc may have different conventions, but generally, some conventions are:

(For C# the conventions are a bit more complex official conventions here).

Code Style Conventions

Similar to naming conventions, but for the syntax of the program.

In C#, for example, often, the starting brackets get their own entire lines :^) - in a lot of other languages, the convention tends to be to keep the starting brackets with the statements before them.

1:

if (you.hasAnswer()) {
    you.postAnswer();
} else {
    you.doSomething();
}

2:

if (you.hasAnswer())
{
    you.postAnswer();
}
else
{
    you.doSomething();
}

(and other variants)

In terms of python, there is an extensive official coding style convention defined, called PEP 8. Info here.

Constants

Potential scenarios where may be appropriate:

• Store program’s build version
• Internal program config

Task 1

In your chosen language declare and assign a value to variables for the following:

A student record that would contain the name, age, gender and the total number of lessons they have attended in their whole time at school

Once this is complete, take a screenshot showing each variable value printed to the console

from enum import Enum

class Gender(Enum):
    UNKNOWN = 0
    MALE = 1
    FEMALE = 2
    OTHER = 3

class Student:
    def __init__(self,
                 name='unnamed',
                 age=-1,
                 gender=Gender.UNKNOWN,
                 lessons_count=-1):
        self.name = name
        self.age = age
        self.gender = gender
        self.lessons_count = lessons_count

    def print(self):
        just = 20
        print(('Name:').ljust(just) + str(self.name))
        print(('Age:').ljust(just) + str(self.age))
        print(('Gender:').ljust(just) + str(self.gender.name))
        print(('Lessons Count:').ljust(just) + str(self.lessons_count))


bob = Student(name="Bob", age=16, gender=Gender.MALE, lessons_count=3)
bob.print()

Explanation

• Enum base class is imported from enum standard library
• Gender class defined, sub-classing Enum.
  • This is done because gender is intrinsically a categoric data type
  • some categories are defined and have IDs assigned, which internally represent them.
• Student class defined - serves as the record.
  • Constructor defined - the code that runs upon instantiation of the class
    • Some parameters are defined to be accepted in the constructor signature
      • have some default values
    • In body of constructor, attributes (fields) of the class is defined, and are instantiated by the parameter values.
  • Print method defined
    • just - a variable used for text justification, to make the output look pretty
    • Each of the attributes are printed
• Instance of Student called bob is instantiated, with some parameters
• the print method of the instance is called, so as to print the attributes, as asked in the question.

Output

Name:               Bob
Age:                16
Gender:             MALE
Lessons Count:      3

Task 2

Data types examples

number = 1
string = 'seven'
Boolean = True
Groceries = ['apple', 'pear', 'Lego']
number2 = 3.141

Data types can essentially be split into integral, numerical, squential and other categories. (See above table).

In the string section just now ASCII was mentioned. Here are some glyphs defined by ASCII and their respective values:

Task 3

Declare a new data type, assign values to the variables and screenshot evidence of the code and printout to the console

class NewType:
    def __init__(self):
        self.a=2
inst=NewType()
inst.a=923
print(inst.a)

user defined types’ behaviour achieved with class instances

Here, the class ‘NewType’ is defined with attribute ‘a’ which is initialised to some value. Demonstration of instantiating that class and replacing attribute ‘a’ with some other variable + demonstration of attribute access.

Task 4

Write a program that asks the user for their name and greets them with their name (you will need to use a scanner to read from the keyboard).

print("Hello, "+input("Please enter your name: "))

Explanation

• Get user input from terminal
• append that to the string "Hello, "
• print the concatenated string

Write a program that asks the user for 2 numbers, stores them and prints the sum of the numbers

num1=int(input("Enter a number: "))
num2=int(input("Enter a number: "))
print(num1+num2)

Explanation

• initialise a variable num1: from user input casted to an integer type, given the prompt "Enter a number".
• ’’ num2 ‘’
• output the sum of the two variables

Write a program that prints a multiplication table for numbers up to 12 (loop).

for i in range(13):
    print(str(i)+" times tables: ")
    for j in range(13):
        print(str(i)+"x"+str(j)+"=="+str(i*j))
    input("press enter to continue")

Explanation

• for each stage as i varies from 0 to 12, being incremented by 1 each iteration, do the following:
  • print i prepended to the string " times tables: "
  • for each stage as j varies from 0 to 12, being incremented by 1 each iteration, do the following:
    • print i concatenated with "x" concatenated with j concatenated with "==" concatenated with the product of i and j

Write a program that prints the next 20 leap years (loop).

from datetime import datetime
cur_year=datetime.now().year
for i in range(cur_year, cur_year+(20*4)+1):
  if i%4==0: print(i)

Explanation

Mod:

The modulus function mod(a, b), represented in most languages through the use of the infix operator % like a % b, gives the remainder after the integer division of a by b. This means that if a % b is equals to 0, for any values of a and b, it can be concluded that a is fully divisible by b.

• as the variable i ranges from the current year (2018) to the year +(20*4):
  • it is checked whether mod(i,4) is 0, which would imply that i is fully divisible by 4 - and so i is a leap year.
  • If this is the case, i is outputted.

Write a guessing game where the user has to guess a secret number. After every guess the program tells the user whether their number was too large or too small. At the end the number of tries needed should be printed.

attempts_limit=10
attempts=1
num=random.randint(0,100)
print("My number is between 0 and 100. Try guess it.")
while True:
    guess=int(input("Enter a guess: "))
    if attempts>=attempts_limit: # extension
        print("You ran out of attempts ("+str(attempts)+")")
        break
    if guess>num:
        print("Too high~")
    elif guess<num:
        print("Too low~")
    else:
        print("Yep~")
        print("It took you " + str(attempts) + " attempts")
        break
    attempts+=1

Explanation

• a random number is generated
• the while loop keeps looping until the number is guessed, or until the attempts limit is reached, at which point the loop is broken.
• At each loop, a guess is inputted through the terminal. If it is not correct, the program outputs whether the guess is too high or low using the > and < comparison operators.

Write a program that computes the reversal of a string. For example, reverse(“I am testing”) should return the string “gnitset ma I”.

print(''.join(list(reversed(input("Enter a string to reverse: ")))))

Explanation

• reversed(..) returns a generator for the reversed list from a list (remember that a string is internally a list)
• since it returns a generator, it must be converted into a list like so: list(reversed(..))
• ''.join(..) joins a list of strings into one big string. This is used because the previous bullet point meant that a list of strings (each representing 1 character) is returned.

EOC Tasks

Questions

Two reasons why meaningful variable names

So that both you and other people can more easily understand what is going on in your code.

Examples to explain difference between constant and variable

A constant cannot be changed at program runtime, whereas variables can. Defining variables that don’t change as constants may result in code being more optimised, so constants should be used as much as possible for variables that don’t change at runtime. An example usage would be the program’s build version. An example of a non-constant variable, however, for example, would be the number of tables in a room. What if someone takes a table out of the room and you have to update the variable? :^)

Why important to declare all variables + constants at start of program

Global variables, and constants should definitely be defined near the top of a program, or the specific scope, so that you can easily see which such variables you have defined when working on your program. More broadly, it also should for the purpose of adhering to good coding practices and conventions, for the sake of making your code more readable (for not just you but others).

Difference between value and variable.

The word ‘variable’ is commonly used to refer to the name given to a specific piece of data and also the piece of data itself. The word ‘value’, however, is usually used solely when referring to the data itself.

Suggest types and names for all of the following:

• current rate of vat

• today’s date

• total takings from shop
• dob
• which wrist person wears watch on

1. VAT_RATE, decimal
   • name follows constant naming conventions
   • decimal because decimal provide good accuracy when working with base-10 decimal numbers, such as the values for VAT
2. cur_date, DateTime
   • name follows snake_case naming convention
   • Most languages provide classes for things like this - in python, it is DateTime
3. tot_takings, Decimal
   • (same as above)
   • (same as above)
4. wear_pos, Enum
   • (same as above)
   • Please do not: “adapt a Boolean variable so that Right was stored as True and Left as False” as the textbook says because that is not scalable at all and is quite unintuitive - unless you named the variable something like “wear_on_right”, which makes sense to either be True or False.
   • Enum: A set of unique named values. In other words, the data-type will be a category, in a sense, out of a defined set of categories. These categories may be “Left” and “Right”.

Research Tasks

n dimensional arrays

1. An array = a data structure used for holding multiple values/objects elements (see above).
2. An instance of an array is an object.
3. This means you can put it inside an array.
4. Put arrays inside arrays
5. Now you have a 2-dimensional array
6. repeat from step 3 until you have an n-dimensional array where n is any number you want
7. ???
8. profit

# array
a=[ 
]
# 2 dimensional array
a=[
    [],
    [],
    ...,
    []
]
# 3 dimensional array
a=[
    [
        [],
       	[],
        ...,
        []
    ],
    ...
]

# .
# .
# .
# n dimensional array
a=[
    ...
]

Built-in Data-Types

See top of the page.