Vocab

  • algorithm: a set of instructions that can accomplish a specific task
  • variables: a method to store data

What is an Algorithm?

a set of instructions that can accomplish a specific task

3 Components of an Algorithm

  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.

Representing Algorithms

  1. Flowcharts: Use shapes and arrows to represent the steps of an algorithm.
  2. Pseudocode: A blend of human language and coding format.

Arithmetic Operations

Subtraction - represented by "-"

num1 = 2 - 1

Addition - Represented by "+"

num1 = 2 + 1

Multiplication - Represented by “*”

num1 = 2 * 1

Division - Represented by “/”

num1 = 2 / 1

Getting the Remainder - Represented by “MOD” (% in python)

num1 = 5 % 2

Application of Mathematical Expressions

Note: collegeboard pseudocode starts at 1
  1. items can be numbers or variables
num1 = 10 # "num1", "num2", etc. are variables
num2 = num1 - 25 # we can perform mathematical expressions on the variables as well
num3 = 100 * num1
num4 = num1 / num2
num5 = 9 % num4
  1. order of operations (same as in normal math)
num1 = 9 % 2 * ( 8 - 2 ) + 8 / ( 6 - 4 )
print(num1) # should print 10

10.0

Variables

4 Different Ways to Store Variables

  1. Numerical value stored in a variable

ex. score = 0

  1. Value of another variable stored in a variable

ex. score = newScore

  1. Performing mathematical expressions on a variable/Result of an operation stored in a variable

ex. score = newScore + 1

  1. Result of a procedure call stored in a variable

ex. avgScore = allScores(20, 60, 80)

Sequencing

  • every time a new value is assigned to a variable, it overrides the last value which was assigned to the same variable
  • changing order of steps changes overall outcome
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 - AP Exam Question

  • make sure to account for every time a variable changes when writing code
var1 = 9
var2 = 7
var3 = 2

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

print(var1) # question would ask something like, what's the value of var1, var2, and var3
print(var2)
print(var3)

7
6
7.0

Strings

  • A string is a collection of characters. What is a character as character can be anything from numbers, letters, spaces, special symbols, etc
  • Certain procedures may be used with strings and they vary from programming language to language Python examples

String Commands for AP Exam Pseudocode

  • len() to find the length of a string
  • lower() to convert to lowercase
  • concat() returns a string made up of the concatenated
  • substring() returns the characters from the string beginning at the at the first position to the last

Substring Example

substring("abcdefghijkl", 2, 5) would print bcde

String Concatenation

  • combining 2 or more strings to make a new strings in order to create a new string

Example of String Concatenation

concat("cookie", "monster") returns cookiemonster

Substrings

  • a part of an already existing string

Example of Substrings

concat("My dogs are cute" 1,2) would return My