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# Notes from Assignment 0 Videos
## Tenets of OOP - https://www.freecodecamp.org/news/object-oriented-programming-concepts-21bb035f7260/
- Four principles: **encanpsulation**, **abstraction**, **inheritance**, **polymorphism**
### Encapsulation
- When an object has private and public states/functions/methods
- Example: A "Cat" class
- The class may have private fields, such as mood, hunger, and energy, and a private function `meow()`
- The class may have three public functions/methods
- `sleep()` will increase the object's energy and hunger
- `play()` will increase the object's mood, decrease its energy, and call the private `meow()` function
- `feed()` will decrease the object's hunger, increase its mood, and call the private `meow()` function
### Abstraction
- Concept that objects should only expose high-level mechanisms
- Natural extension of Encapsulation concept
- Concept can be seen in real life, for example, a water cooler
- There is technology going on under the hood, but the end user only sees the lever to pull for water
- Another example: smartphone
- Very complicated under the hood, but at a high level, there is only the home button, volume buttons, and charge input
### Inheritance
- Idea to combat the problem that often times, many objects are similar but differ slightly
- Involves creating a parent class and a child class, which is derived from the parent
- Example: We can have a Person class with a name and an email
- Then we can define a Teacher, which has all the fields from the Person class, plus an additional subject field
- We could create child classes from Teacher for Private Teacher and Public Teacher, which inherit the teacher fields with their own fields as well
- We could also define a Student, which has all the fields from the Person class, plus additional class and grades fields
### Polymorphism
- Creating a method in a parent that differs slightly between child classes that inherit this method
- Example: There is a Shape parent class that has the method `CalculateArea()`
- The child classes are Triangle, Circle, and Rectangle, so each child class will have its own implementation of the `CalculateArea()` method
---
## C++ Data Types - https://www.softwaretestinghelp.com/data-types-in-cpp/
- C++ supports two types of data
- Primitive/Standard data types
- User-defined data types
### Primitve or Standard Data Types
|Data Type |C++ Keyword|Value Type |
|--------------|-----------|--------------------------------------|
|Character |char |Character (ASCII values) |
|Integer |int |Numeric whole numbers |
|Floating point|float |Decimal values with single precision |
|Decimal point |double |Double precision floating point values|
|Boolean |bool |True or false |
|void |void |Valueless (no value) |
|Wide character|wchar_t |Character including Unicode strings |
- Primitves can also be modified in memory length using the following data modifiers:
- signed
- unsigned
- short
- long
### User-defined Data Types
- **Typedef**
- Sets an alias for another data type
- Example:
- `typedef int age;`
- The above code creates an alias `age` for the `int` data type
- **Enumeration**
- Example:
- `enum daysOfWeek {Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday};`
- The above code creates a data type `daysOfWeek`. It recognizes all the above keywords (they are really aliases for integer values 0, 1, 2, etc.)
- Boolean is, in theory, an enumeration, since it recognizes the keywords true and false
- C++ example:
```
#include <iostream>
using namespace std;
enum daysOfWeek {Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday};
int main(){
daysOfWeek today;
today = Thursday;
cout << "This is day " << today << " of the week";
return 0;
}
---
//output:
This is day 4 of the week
```
- **Class**
- Collection of objects
- Example: a Student class:
```
class student{
char *name;
int age;
public:
void printDetails(){
cout << "Name: " << name;
cout << "Age: " << age;
}
}
```
- **Structure**
- A Structure is like a Class, but does not support methods (it can only have variables as its members)
- A Class is really just a structure that can support both variables and methods
- Example:
```
struct employee{
char name[50];
float salary;
int empId;
};
```
## What C++ is and Why - https://www.youtube.com/watch?v=tbNe-3FXqFM
### C++ in two lines
- Direct map to hardware
- of infrastructure and fundamental data types
- Initially from C
- Future: use novel hardware better (caches, multicores, GPUs, FPGAs, SIMD, ...)
- Zero-overhead abstraction
- Classes, inheritance, generic programming, ...
- Initially from Simula (where it wasn't zero overhead)
### What really matters?
- People
- A programming language is a tool, not an end goal
- "Ordinary people" want great systems, not programming languages
- Software developers want great tools
- not just programming language features
### The onion principle
- Management of complexity
- Make simple things simple!
- Layer of abstraction
- The more layers you peel off the more you cry
### An engineering approach
- Principled and pragmatic design
- Progress gradually guided by feedback
- There are always many tradeoffs
- Choosing is hard
- Design decisions have consequences
- Determine what kind of applications can be done well
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