Exercise 4

 

These exercises are about logical operators and reading/writing from Session 2.

Exercise 1 - If Else

• Build an if statement that test if x is a negative number. Write a print statement that will confirm if x is less than 0. Test it with several values of x.

x=42

if x<0:
  print("It's a negative number!")

x=-42

if x<0:
  print("It's a negative number!")

## It's a negative number!

• Modify the previous if statement to include an else. Ensure a print statement is returned to say if the number is not negative.

x=0

if x<0:
  print("It's a negative number!")
else:
  print("It's not a negative number!")

## It's not a negative number!

x=-1

if x<0:
  print("It's a negative number!")
else:
  print("It's not a negative number!")

## It's a negative number!

• Finally add a elif statement. We want a response to confirm if x is negative, positive or if it is zero.

x=-1

if x<0:
  print("It's a negative number!")
elif x==0:
  print("It's zero")
else:
  print("It's a positive number!")

## It's a negative number!

  
x=0

if x<0:
  print("It's a negative number!")
elif x==0:
  print("It's zero")
else:
  print("It's a positive number!")

## It's zero

  
x=1

if x<0:
  print("It's a negative number!")
elif x==0:
  print("It's zero")
else:
  print("It's a positive number!")

## It's a positive number!

• Build an if/else statement that test if a variable is odd/even. Include x in the printed output.

Hint1: x will likely be an integer so it will need to be coerced to print out as part of a message string. Hint2: The modulus operator may be useful here i.e. x%2 returns the remainder after the value of x is divided by 2.

x=1

if x%2==0:
  mymessage = str(x) + " is even"
  print(mymessage)
else:
  mymessage = str(x) + " is odd"
  print(mymessage)

## 1 is odd

  
  
x=42

if x%2==0:
  mymessage = str(x) + " is even"
  print(mymessage)
else:
  mymessage = str(x) + " is odd"
  print(mymessage)

## 42 is even

• Put this in a function and try out it out on various variables.

def even_or_odd(x):
  if x%2==0:
    mymessage = str(x) + " is even"
    print(mymessage)
  else:
    mymessage = str(x) + " is odd"
    print(mymessage)

even_or_odd(10)

## 10 is even

even_or_odd(3)

## 3 is odd

even_or_odd(10007)

## 10007 is odd

Exercise 2 - Loops

• Calculate the factorial (factorial of 3 = 3 * 2 * 1) of 10 using a loop. Hint: first try to write some pseudocode to help you build this

# Idea
Each iteration of a loop I want to multiply my factorial by itself:
x=1  result_1 = 1
x=2  result_2 = result_1*x = 2*1
x=3  result_3 = result_2*x = 3*2*1
x=4  result_4 = result_3*x = 4*3*2*1
etc...

# Pseudocode

for 0 to 9:
  if x is 0:
    create an object and set its value to 1
  else:
    once we are past the first data point we can multiply factorialAnswer by the iteration we are on. Then overwrite factorialAnswer with this result. 

for x in range(9):
  if x == 0:
    factorialAnswer = 1
  else:
    factorialAnswer = factorialAnswer * (x+1)

factorialAnswer

## 362880

• Adjusting your answer from before, what is the first number that has a factorial greater than 1000? Hint: A while loop will be good for this

factorialAnswer = 0
count = 0

while factorialAnswer <= 1000:
  if count == 0:
    factorialAnswer = 1
  else:
    factorialAnswer = factorialAnswer * (count+1)
  count = count+1
    
    

count

## 7

factorialAnswer

## 5040