Problem Solving & Review

CSCI 1012

Announcements

• Unit 1 Exam: 6 Oct
  • 1957 E St. Room 113 3:45-5:00 PM
  • 60 minutes
  • One side of one page (standard Letter) of notes
  • Similar format to quizzes
• DSS: See me!

In-Class Exercises

• File names:
  • sum_check.py
  • fibonacci.py
  • two_dice.py
• Turn in on the submit server before the end of lecture for credit
• Turn in one .zip with all the .py files
  • Unlimited attempts during lecture
• We’ll provide solutions – pay attention!

Today

• Review
• Problem Solving

Operators

Operator	Function (with numbers)
+	Addition
-	Subtraction
*	Multiplication
/	Division
**	Exponentiation
//	Quotient
%	Remainder

Tracing Example - Operators

x = 2
x = 3 + x
y = x // 2
z = x + 1
z = z + y
print(z)

Ints, Floats, and Strings

Does this work?

s = ""
a = 3
s = s + a

Ints, Floats, and Strings

s = "1"
a = 3
s = s + a
print(a)
print(s)

Ints, Floats, and Strings

s = "1"
a = 3
s = s + str(a)
a = a + int(s)
print(a)
print(s)

Functions

def function_name(arg1, arg2):
  # function body
  # code to execute
  return

# this is outside the function

Function - Tracing

def func(a, b):
  a = a + b
  if a > b:
    return a
  return b

x = func(-1, -2)
y = func(2, 2)
print(x + y)

Exercise 1

sum_check.py

def sum_check(A, B, C):
  # your code here!

• Arguments A, B, and C will be ints
• Return bool True if any two args sum to the third
  • Otherwise, return False

Examples:

• sum_check(1, 3, 4) returns True
• sum_check(2, 3, 4) returns False
• sum_check(0, 0, 0) returns True

Functions Calling Functions

def funcA(argA):
  return argA + 1

def funcB(argB):
  C = funcA(argB)
  return C * 2

z = funcB(3)
print(z)

Review: Comparison Operators

Operator	Function	Syntax
==	Equal?	3 == 5
!=	Not equal?	3 != 5
<	Less than?	3 < 5
>	Greater than?	3 > 5
<=	Less than or equal to	3 <= 5
>=	Greater than or equal to?	3 >= 5

Conditionals

• if
  • Starts the conditional block, necessary
  • Only one allowed
• elif (“else if”)
  • Zero or more allowed
  • Checked in sequence
• else
  • Always

Iteration

• while loop
  • superficially similar to if
  • watch out for infinite loops!
• for loop
  • range function

• 1 argument: “stop”
• 2 arguments: “start,” “stop”
• 3 arguments: “start,” “stop,” “skip”

Exercise 2

fibonacci.py

def fibonacci(n):
  # your code here!

• Return a string consisting of the fibonacci sequence values less than argument n
  • Separate numbers with spaces
  • Argument will always be at least 2

Examples:

• fibonacci(12) returns string '1 1 2 3 5 8'
• fibonacci(30) returns string '1 1 2 3 5 8 13 21'

Exercise 3 🎲 🎲

two_dice.py

def two_dice(m):
  # your code here!

Return how many ways there are to get the sum of two 6-sided dice to add to the argument.

Examples:

• two_dice(1) returns 0
• two_dice(2) returns 1 (1+1)
• two_dice(3) returns 2 (1+2, 2+1)
• two_dice(4) returns 3 (1+3, 3+1, 2+2)

Next Week

❗ Exam on 6 October. (in lecture)

Homework 6 due Sunday, 5 Oct 11:55 PM

• Late days allowed…
• Material might be on exam