6.00.1x - Week 1

1.1 Introduction:
Machine are good at calculations and remember results.
Some problems require better algorithm to solve faster.
Some problems are fundamentally hard:turing halting or decrypt encryption which is benefical for us.

1.1 Knowledge
Declarative knowledge: statement of fact
Imperative knowledge: recipe, how to solve
Algorithm = sequence of steps + flow of control + when/how to stop

1.2 Machines
Fixed program vs. Stored program
Core of machine: Memory, Arithmetic Logic Unit (ALU), and Control Unit with program counter
Interpreter vs Compiler: read 1
Turing machine: infinite tape, 6 primitives: move left, move right, scan, read, write, do nothing
Anything computable in one language is computable in any other programming language

1.3 Languages
Expression: legal combination of primitives
Syntax: combination of primitives that makes sense, legal expression
Static semantics: valid syntax that has meaning
Semantic: meaning associated with a syntactically correct expression with no static semantic errors
Reference: Quora, read 1

1.4 Types
Program: sequence of definitions and commands
Commands (statements): instruct interpreter to do something
Objects: scalar (can't be subdivided) or non-scalar (have internal structured)
Scalar objects: int, float, bool, NoneType
Division will return float
Operation precedence: **, * or / or //, + or -, left to right

1.5 Variables
Can bind (assign) and re-bind (re-assign) variable names
In programming, you do not "solve for x"

1.6 Operators and Branching
if, elif, else

2.1 Bindings
keywords - will have a different color when typed in IDE

2.2 Strings
String is non-scalar object. Casting: str(2.5) = '2.5'
letters, special characters, spaces, digits in single quotes or double quotation marks
3 * 'eric' = 'ericericeric'
len('eric') = 4, 'eric'[0] = 'e', 'eric'[1:3] = 'ri' (excluding last index), 'eric'[:3] = 'eri', 'eric'[1:] = 'ric'
'eric'[:] = 'eric' (a copy, not original string), 'a' in 'hat' = True
string[start:stop:step]

2.3 Input/Output
text = input("whatever typed will be saved into text")

2.4 IDEs
Spyder (comes with Anaconda) - shortcut F5 to Run

2.5 Control Flow
while vs for loops: can rewrite a for loop using a while loop, the other way not always correct
range(5): 0 to 4 - up to but not including. range(5, 7) = 5, 6. range(0, 6, 2) = 0, 2, 4
break vs continue
del(str): clear whatever value attached to str
Ctrl + c: to stop infinite loop




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