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Monday, 26 October 2020

October 26, 2020

First Programming Concepts Cheat Sheet

 


First Programming Concepts Cheat Sheet

Functions and Keywords

Functions and keywords are the building blocks of a language’s syntax.

Functions are pieces of code that perform a unit of work. In the examples we've seen so far, we've only encountered the print() function, which prints a message to the screen. We'll learn about a lot of other functions in later lessons but, if you're too curious to wait until then, you can discover all the functions available here.

Keywords are reserved words that are used to construct instructions. We briefly encountered for and in in our first Python example, and we'll use a bunch of other keywords as we go through the course. For reference, these are all the reserved keywords:

Falseclassfinallyisreturn
Nonecontinueforlambdatry
Truedeffromnonlocalwhile
anddelglobalnotwith
aselififoryield
assertelseimportpass
breakexceptinraise

You don't need to learn this list; we'll dive into each keyword as we encounter them. In the meantime, you can see examples of keyword usage here.

Arithmetic operators

Python can operate with numbers using the usual mathematical operators, and some special operators, too. These are all of them (we'll explore the last two in later videos).

  • a + b = Adds a and b
  • a - b = Subtracts b from a
  • a * b = Multiplies a and b
  • a / b = Divides a by b
  • a ** b = Elevates a to the power of b. For non-integer values of b, this becomes a root (i.e. a**(1/2) is the square root of a)
  • a // b = The integer part of the integer division of a by b
  • a % b = The remainder part of the integer division of a by b
October 26, 2020

What is Programming?

Programming is, quite literally, all around us. From the take-out we order to the movies we stream, code enables everyday actions in our lives. Tech companies are no longer recognizable as just software companies — instead, they bring food to our door, help us get a taxi, influence outcomes in presidential elections, or act as a personal trainer.


When you’re walking down the street, where can you find technology in your environment? Click on the white circles.


…AND PROGRAMMING IS FOR EVERYONE

For many years, only a few people have known how to code. However, that’s starting to change. The number of people learning to code is increasing year by year, with estimates of around 22.3 million software developers worldwide, which doesn’t even account for the many OTHER careers that relate to programming.

Here at Codecademy, our mission is to make technical knowledge accessible and applicable. Technology plays a crucial role in our economy — but programming is no longer just for software engineers. Any person can benefit from learning to program — whether it’s learning HTML to improve your marketing emails or taking a SQL course to add a dose of analysis to your research role.

Even outside of the tech industry, learning to program is essential to participating in the world around you: it affects the products you buy, the legal policies you vote for, and the data you share online.

So, let’s dig into what programming is.

WHAT IS PROGRAMMING?

Put simply, programming is giving a set of instructions to a computer to execute. If you’ve ever cooked using a recipe before, you can think of yourself as the computer and the recipe’s author as a programmer. The recipe author provides you with a set of instructions that you read and then follow. The more complex the instructions, the more complex the result!

How good are you at giving instructions? Try and get Codey to draw a square!


PROGRAMMING AS COMMUNICATION, or CODING

“Ok, so now I know what programming is, but what’s coding? I’m here to learn how to code. Are they the same thing?”

While sometimes used interchangeably, programming and coding actually have different definitions.

  • Programming is the mental process of thinking up instructions to give to a machine (like a computer).
  • Coding is the process of transforming those ideas into a written language that a computer can understand.

Over the past century, humans have been trying to figure out how to best communicate with computers through different programming languages. Programming has evolved from punch cards with rows of numbers that a machine read, to drag-and-drop interfaces that increase programming speed, with lots of other methods in between.

pictures of different punchcards

via GIPHY

To this day, people are still developing programming languages, trying to improve our programming efficiency. Others are building new languages that improve accessibility to learning to code, like developing an Arabic programming language or improving access for the blind and visually impaired.

PROGRAMMING AS COLLABORATION

“The problem with programming is not that the computer isn’t logical—the computer is terribly logical, relentlessly literal-minded.”

Ellen Ullman, Life in Code

When we give instructions to a computer through code, we are, in our own way, communicating with the computer. But since computers are built differently than we are, we have to translate our instructions in a way that computers will understand.

Computers interpret instructions in a very literal manner, so we have to be very specific in how we program them. Think about instructing someone to walk. If you start by telling them, “Put your foot in front of yourself,” do they know what a foot is? Or what front means? (and now we understand why it’s taken so long to develop bipedal robots…). In coding, that could mean making sure that small things like punctuation and spelling are correct. Many tears have been shed over a missing semicolon (;) a symbol that a lot of programming languages used to denote the end of a line.

But rather than think of this as a boss-employee relationship, it’s more helpful to think about our relationship with computers as a collaboration.

The computer is just one (particularly powerful) tool in a long list of tools that humans have used to extend and augment their ability.

As mentioned before, computers are very good at certain things and well, not so good at others. But here’s the good news: the things that computers are good at, humans suck at, and the things that computers suck at, humans are good at! Take a look at this handy table:

table comparing human and computer abilities

Just imagine what we can accomplish when we work together! We can make movies with incredible special effects, have continuous 24/7 factory production, and improve our cities and health.

picture of a robot-human

via GIPHY

The best computer programs are the ones that enable us to make things that we couldn’t do on our own, but leverage our creative capacities. We may be good at drawing, but a computer is great at doing the same task repeatedly — and quickly!


CONCLUSION

As programming becomes a larger part of our lives, it’s vital that everyone has an understanding of what programming is and how it can be used. Programming is important to our careers, but it also plays a key role in how we participate in politics, how we buy things, and how we stay in touch with one another.

Learning to code is an exciting journey. Whether your goal is to build a mobile app, search a database, or program a robot, coding is a skill that will take you far in life. Just remember — computers are tools. While learning to the program may initially be frustrating, if you choose to stick with it, you’ll be able to make some brilliant things.


Reshared: https://www.codecademy.com/

Wednesday, 22 July 2020

July 22, 2020

Learn C++ References & Pointers


const Reference

In C++, pass-by-reference with const can be used for a function where the parameter(s) won’t change inside the function.
This saves the computational cost of making a copy of the argument.

int triple(int const &i) { return i * 3; }

Pointers

In C++, a pointer variable stores the memory address of something else. It is created using the * sign.

int* pointer = &gum;

References

In C++, a reference variable is an alias for another object. It is created using the & sign. Two things to note:
  1. Anything done to the reference also happens to the original.
  2. Aliases cannot be changed to alias something else.

int &sonny = songqiao;

Memory Address

In C++, the memory address is the location in the memory of an object. It can be accessed with the “address of” operator, &.
Given a variable porcupine_count, the memory address can be retrieved by printing out &porcupine_count. It will return something like: 0x7ffd7caa5b54.

std::cout << &porcupine_count << "\n";

Dereference

In C++, a dereference reference operator*, can be used to obtain the value pointed to by a pointer variable.

int gum = 3; // * on left side is a pointer int* pointer = &gum; // * on right side is a dereference of that pointer int dereference = *pointer;

Pass-By-Reference

In C++, pass-by-reference refers to passing parameters to a function by using references.
It allows the ability to:
  • Modify the value of the function arguments.
  • Avoid making copies of a variable/object for performance reasons.

void swap_num(int &i, int &j) { int temp = i; i = j; j = temp; } int main() { int a = 100; int b = 200; swap_num(a, b); std::cout << "A is " << a << "\n"; std::cout << "B is " << b << "\n"; }

Thursday, 2 July 2020

July 02, 2020

Learn Python: Syntax

Comments

A comment is a piece of text within a program that is not executed. It can be used to provide additional information to aid in understanding the code.
The # character is used to start a comment and it continues until the end of the line.

# Comment on a single line user = "JDoe" # Comment after code

Arithmetic Operations

Python supports different types of arithmetic operations that can be performed on literal numbers, variables, or some combination. The primary arithmetic operators are:
  • + for addition
  • - for subtraction
  • * for multiplication
  • / for division
  • % for modulus (returns the remainder)
  • ** for exponentiation

# Arithmetic operations result = 10 + 30 result = 40 - 10 result = 50 * 5 result = 16 / 4 result = 25 % 2 result = 5 ** 3

Plus-Equals Operator +=

The plus-equals operator += provides a convenient way to add a value to an existing variable and assign the new value back to the same variable. In the case where the variable and the value are strings, this operator performs string concatenation instead of addition.
The operation is performed in-place, meaning that any other variable which points to the variable being updated will also be updated.

# Plus-Equal Operator counter = 0 counter += 10 # This is equivalent to counter = 0 counter = counter + 10 # The operator will also perform string concatenation message = "Part 1 of message " message += "Part 2 of message"

Variables

A variable is used to store data that will be used by the program. This data can be a number, a string, a Boolean, a list or some other data type. Every variable has a name which can consist of letters, numbers, and the underscore character _.
The equal sign = is used to assign a value to a variable. After the initial assignment is made, the value of a variable can be updated to new values as needed.

# These are all valid variable names and assignment user_name = "@sonnynomnom" user_id = 100 verified = False # A variable's value can be changed after assignment points = 100 points = 120

Modulo Operator %

A modulo calculation returns the remainder of a division between the first and second number. For example:
  • The result of the expression 4 % 2 would result in the value 0, because 4 is evenly divisible by 2 leaving no remainder.
  • The result of the expression 7 % 3 would return 1, because 7 is not evenly divisible by 3, leaving a remainder of 1.

# Modulo operations zero = 8 % 4 nonzero = 12 % 5

Integers

An integer is a number that can be written without a fractional part (no decimal). An integer can be a positive number, a negative number or the number 0 so long as there is no decimal portion.
The number 0 represents an integer value but the same number written as 0.0 would represent a floating point number.

# Example integer numbers chairs = 4 tables = 1 broken_chairs = -2 sofas = 0 # Non-integer numbers lights = 2.5 left_overs = 0.0

String Concatenation

Python supports the joining (concatenation) of strings together using the + operator. The + operator is also used for mathematical addition operations. If the parameters passed to the + operator are strings, then concatenation will be performed. If the parameter passed to + have different types, then Python will report an error condition. Multiple variables or literal strings can be joined together using the + operator.

# String concatenation first = "Hello " second = "World" result = first + second long_result = first + second + "!"

Errors

The Python interpreter will report errors present in your code. For most error cases, the interpreter will display the line of code where the error was detected and place a caret character ^ under the portion of the code where the error was detected.

if False ISNOTEQUAL True: ^ SyntaxError: invalid syntax

ZeroDivisionError

A ZeroDivisionError is reported by the Python interpreter when it detects a division operation is being performed and the denominator (bottom number) is 0. In mathematics, dividing a number by zero has no defined value, so Python treats this as an error condition and will report a ZeroDivisionError and display the line of code where the division occurred. This can also happen if a variable is used as the denominator and its value has been set to or changed to 0.

numerator = 100 denominator = 0 bad_results = numerator / denominator ZeroDivisionError: division by zero

Strings

A string is a sequence of characters (letters, numbers, whitespace or punctuation) enclosed by quotation marks. It can be enclosed using either the double quotation mark " or the single quotation mark '.
If a string has to be broken into multiple lines, the backslash character \ can be used to indicate that the string continues on the next line.

user = "User Full Name" game = 'Monopoly' longer = "This string is broken up \ over multiple lines"

SyntaxError

A SyntaxError is reported by the Python interpreter when some portion of the code is incorrect. This can include misspelled keywords, missing or too many brackets or parenthesis, incorrect operators, missing or too many quotation marks, or other conditions.

age = 7 + 5 = 4 File "<stdin>", line 1 SyntaxError: can't assign to operator

NameError

A NameError is reported by the Python interpreter when it detects a variable that is unknown. This can occur when a variable is used before it has been assigned a value or if a variable name is spelled differently than the point at which it was defined. The Python interpreter will display the line of code where the NameError was detected and indicate which name it found that was not defined.

misspelled_variable_name NameError: name 'misspelled_variable_name' is not defined

Floating Point Numbers

Python variables can be assigned different types of data. One supported data type is the floating point number. A floating point number is a value that contains a decimal portion. It can be used to represent numbers that have fractional quantities. For example, a = 3/5 can not be represented as an integer, so the variable a is assigned a floating-point value of 0.6.

# Floating point numbers pi = 3.14159 meal_cost = 12.99 tip_percent = 0.20

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print() Function

The print() function is used to output text, numbers, or other printable information to the console.
It takes one or more arguments and will output each of the arguments to the console separated by a space. If no arguments are provided, the print() function will output a blank line.

print("Hello World!") print(100) pi = 3.14159 print(pi)