Algorithm

An Algorithm is a set of instructions that can accomplish a specific test

Types of Algorithms

  1. Sequencing: Algorithms do tasks in the order of specification.
  2. Selection: Helps choose two different outcomes based off a decision.
  3. Iteration: If a condition is true, then the code can repeat.

Ways to represent Algorithms

  1. Flowcharts: Shapes and arrows represent steps of an algorithms
  2. Pseudocode: Human language + code language

Addition

num1 = 2 + 1

Subtraction

num1 = 2 - 1

Multiplication

num1 = 2 * 1

Division

num1 = 2 / 1

Remainder

num1 = 5 % 2

Other examples such as numbers or variables

num1 = 10
num2 = num1 - 25
num3 = 100 * num1
num4 = num1 / num2
num5 = 9 % num4

Order of Operations

Arithmetic operations in programming are performed in the same order as operations in mathematics:

  • Operations in parentheses should be done first.
  • Division and multiplication should be done before addition and subtraction.
  • Modulus works similar to multiplication and division.
num1 = 9 % 2 * ( 8 - 2 ) + 8 / ( 6 - 4 )
print(num1)

10.0

Variables

Different Ways Values are Stored in Variables

  • Numerical value stored in a variable
  • Value of another variable stored in a variable
  • Result of an operation stored in a variable
  • Result of a procedure call stored in a variable
score = 0   # 1
score = newScore    # 2
score = newScore + 2    # 3
avgScore = allscores(20, 60, 80)    # 4

Changing the order of the steps changes the overall outcome, since every time the value assigned to a variable is changed, it overrides the last value which was assigned to the same variable. That is why it is important to track the value of variables, especially in code where the value is constantly changing.

num1 = 2
num2 = 4
num3 = 6
num1 = num2 + num3      # num1 is now 4 + 6, which is 10
num2 = num1 + num3      # num2 is now (the new num1) 10 + 6, which is 16
# output: num1 = 10, num2 = 16, num3 = 6

vs

num1 = 2
num2 = 4
num3 = 6
num2 = num1 + num3  #num2 is now 8
num1 = num2 + num3  # num1 is now 14
# output: num1 = 14, num2 = 8, num3 = 6

Tracking variables is a common question found on AP exams and is an important thing to keep in mind when writing any code. If the value of your variables changes a lot, not accounting for these changes can result in an unwanted outcome.

var1 = 9
var2 = 7
var3 = 2

#var = var1 + 5
#var2 = var1 - var3
#var1 = var2
#var3 = (var1 + var2) / 2
#var2 = 6

print(var1)
print(var2)
print(var3)

9
7
2

What is a string?

A string is a collection of characters

  • len() will find the length of a list
  • lower() to covert list to lowercase
  • concat() combines two strings

HACKS! 

Num1 = 50
Num2 = Num1 % 9 + 15 # 50/9 = 45 R5, 5+15 = 20
Num3 = Num2 / Num1 + ( Num2 * 2 ) # 20/50 + (20*2) = 40.4
Num4 = Num3 + Num1 / 5 - 10 # 40.4+50 / 5-10 = 40.4
Result = Num4 - Num2 # 40.4-20 = 20.4

The answer for Num4 - Num2 = 20.4

Num1 = 10
Num2 = Num1 % 3 * 4 # 10/3 = R1, 1*4 = 4
Num1 = Num2 # Num1 = 4
Num3 = Num1 * 3 # Num3 = 4, 4*3 = 12
Result = Num3 % 2 # 12 % 2 = 0

The answer for Num3 % 2 = 0

valueA = 4
valueB = 90
valueC = 17
valueB = valueC - valueA # valueB = 17 - 4 = 13
valueA = valueA * 10 # 4 * 10 = 40
if valueB > 10:
    print(valueC) 

17

type = "curly"
color = "brown"
length = "short"
type = "straight"
hair = type + color + length # straight + brown + short
print(hair)

straightbrownshort

Noun = "Mr.Mortenson" 
Adjective = "handsome" 
Adjective2 = "Very" 
Verb = "is" 
abrev = Noun[0:6]
yoda = (Adjective2 + " " + Adjective + " " + abrev + " "+ Verb + ".") 
print(yoda)

Very handsome Mr.Mor is.

bagel = "blueberry" 
bagel2 = "rasin" 
len1 = len(bagel) / 2 
len2 = len(bagel2) * 45 
vote1 = bagel + "vote" + str(len2) 
vote2 = bagel2 + "vote" + str(len1) 
votes = vote1 + " " + vote2
print(votes)

blueberryvote225 rasinvote4.5