# Branching and Iteration

## String

Enclosed in quotation marks or single quotes, exp:
`hi = "hello there"`

notice `" "` is defined as space, exp:

name = ABC
greeting = hi + " " + name
print(greeting)

Difference in printing , and + between objects:

>>> print("hi","chong")
hi chong
>>> print("hi"+"chong")
hichong

## Input: `input("")`
prints whatever is in the quotes, the string user types next will be binded as a variable (input into memory), exp:

>>> text = input("type something down below")
type something down below
hello
>>> print(text)
hello

## Cast: Input For Numbers
binding numbers (only when ur working with numbers):

>>> num = int(input("type a number"))
type a number25
>>> print(5*num)
125

## Comparisons
Only variables, evaluate to a boolean:

i > j
i >= j
i < j
i <= j
i == j  #equality test, True if i is the same as j
i != j  #inequality test, True if i not the same as j

Test:

>>> i = 5
>>> j = 6
>>> i<j
True
>>> i>j
False

## Logic Operators on `boolean`

Assume `a` and `b` are variable names with Boolean values:

| A | B | A and B | A or B |
| - | - | - | - |
| `True` | `True` | `True` | `True`
| `True` | `False` | `False` | `True`
| `False` | `True` | `False` | `True`
| `False` | `False` | `False` | `False`

Logic operators can be used in code to connect variables:
- `not a`
- `True` if `a` is `False`
- `False` if `a` is `True`
- `a and b`
- `True` if both are `True`
- `a or b`
- `True` if either one is `True` or both are `True`

pset_time = 15
sleep_time = 8
print(sleep_time > pset_time)
derive = True
drink = False
both = drink and derive
print(both)

## if else vs elif else (Control Flow and Branching)

if <condition>:
<expression>
<expression>
...
else:
<expression>
<expression>

Decision is made from the condition under if that is true or false, expressions is evaluated or executed when condition is true.

if <condition>:
<expression>
<expression>
...
elif <condition>:
<expression>
<expression>
...
else:
<expression>
<expression>

`elif` is made for a separate condition if the first condition is not `True`. If all are `False`, the last expression under `else` is executed

*see how multiple conditions can have shorter strings of code using elif vs if*

### `if else`

x = float(input("type a number to compare"))
y = float(input("type another number to compare"))
if x > y:
    print("x is bigger")
    print("y is smaller")
if y > x:
    print("y is bigger")
    print("x is smaller")
if x == y:
    print("they're the same!")

### `elif`

x = float(input("type a number to compare"))
y = float(input("type another number to compare"))
if x > y:
    print("x is bigger")
    print("y is smaller")
elif y > x:
     print("y is bigger")
     print("x is smaller")
else:
     print("they're the same!")

# `while` loops

`if else` infinite loops can be turned into `while` loops:

while <condition>:
  <expression>
<expression>

`<condition>` evaluates to a Boolean. If <condition> is `True`, do all the steps inside the `while` code block. Check `<condition>` again, repeat until <condition> it's `False`.

# `for` loops

Acts as a $n = n+1$ loop shortcut, `while` vs `for` below:

n = 0
while n < 5:
print(n)
n = n+1

`for` loop shortcut:

for n in range(5):
print(n)

Each time through the loop, `<variable>` takes a value, first time, `<variable>` starts at the smallest value, next time, `<variable>` gets the prev value + 1
etc. `range()` **creates a sequence from 0 to whatever number u set, in this case it's 0-5**

## Controlling `range()`

`range(start, stop, step)`, default: start = 0, step = 1:

mysum = 0
for i in range(7, 10):
mysum += i
print(mysum)

mysum = 0
for i in range(5, 11, 2):
mysum += i
print(mysum)

*note: doesn't include stop values*

## `break`

`break` acts as an immediate exit from the `while` loop when a condition is met and skips the remaining expressions after, but only exits it's innermost loop:

while <condition_1>:
  while <condition_2>:
    <expression_a>
    break
        <expression_b>
    <expression_c>

Example:

mysum = 0
for i in range(5, 11, 2):
    mysum += i
    if mysum == 5:
      break
    mysum += 1
print(mysum)

Since `i` is 5 inside the for loop, when `mysum += i` occurs `mysum` will equal to 5 as well.

Notice that because `mysum` is 5 so it fits the if block's condition, hence the for loop will break.

## `for` vs `while` loops

| `for` | `while` |
| - | - |
| **know** number of iterations | iterations are **unbounded**
| end early via `break` | end early via `break`
| uses a **counter** | **uses a counter but must initialize before loop and increment it inside loop**
| can rewrite a `for` loop using a `while` loop | may not be able to rewrite a `while` loop using a `for` loop