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Activity 1.2 Arithmetic

Introduction

Math is extremely important in computer science. Any useful program has to store and use numbers in some way. From video games, to online stores, to graphic design apps, math is necessary to creating the software we use every day. It is necessary to not only calculate math expressions, but also to display the results to the user.

print() doesn’t just output text messages, it is also capable of outputting the numbers and math expressions. In this activity, we will writing simple programs to demonstrate how math works in Python. There are multiple symbols used to write math expressions:

• + Addition operator
• - Subtraction operator
• * Multiplication operator
• / Division operator, calculates quotient with decimals
• // Integer division operator, cuts off decimal (Think long division)
• % Modulus (mod) operator, calculates remainer

The symbols for division may throw you off, because they don’t match the traditional arithmetic symbols we use in math class. We’ll practice using them in depth, so you can see how useful it is to divide numbers in different ways.

Skills to Practice

• Write math expressions
• Output numbers with print()
• Document code with single line comments
• Control math calculation with order of operations

Instructions

Setup

1. Create a new Python application. Name the project 1.2 Math.
2. Click Create.

Code

# These are comments. They help programmers take notes in their code.
# Comments are ignored by the compiler.

# Addition
print("I have two apples. I find another apple. How many apples do I have?")
print(2 + 1)
print()

print("Bank balance: $1000. Depositing $500.96. Your new balance is:")
print(1000 + 500.96)
print()

# Subtraction
print("I'm hungry and I want to eat an apple. How many apples will I have left?")
print(3 - 1)
print()

# Multiplication
print("I'm 30 years old. In months, that's: ") # Replace 30 with your age
print(30 * 12) # Replace 30 with your age
print()

# Division - Quotient and remainder

# Quotient
print("We have eight slices of pizza between the two of us.")
print("We each get this many slices: ")
print(8 / 2)
print()

print("I have to split this dollar between the six of us. We each get: ")
print(100 / 6) # Will this divide evenly?
print("Without fractional amounts, this is: ")
print(100 // 6)
print()

# Remainder using the modulus, or mod, operator
print("After splitting up the dollar, how many cents are left over?")
print(100 % 6)
print()

# Order of operations
print("4 * 10 + 12 equals:")
print(4 * 10 + 12)
print("4 * (10 + 12) equals:")
print(4 * (10 + 12))

Debug

I have two apples. I find another apple. How many apples do I have?
3

Bank balance: $1000. Depositing $500.96. Your new balance is:
1500.96

I'm hungry and I want to eat an apple. How many apples will I have left?
2

I'm 30 years old. In months, that's:
360

We have eight slices of pizza between the two of us.
We each get this many slices:
4

I have to split this dollar between the six of us. We each get:
16.666666666666668
Without fractional amounts, this is:
16

After splitting up the dollar, how many cents are left over?
4.0

4 * 10 + 2 equals:
52
4 * (10 + 2) equals:
88

Tips, Tricks, and Reflection

• This program looks terrible. The math for each statement may correct, but it’s hard to read. The division involving money returns a repeating decimal, every answer is on it’s own line, and the monetary values don’t have a dollar sign. These are called formatting issues, and we will learn how to make the output look better in future programs.
• When writing math expressions in code, you don’t have to have a space in between the numbers and signs. It is valid to write 2+2, but I recommend writing 2 + 2 with the spaces in between.
• Math signs + - * / % are known as operators, and numbers used with operators are known as operands. When we write math statements they are called expressions.