Arithmetic operators in Ruby

Introduction

Arithmetic operators help us do math with numbers in programs. They let us add, subtract, multiply, and divide easily.

Calculating the total price of items in a shopping cart.

Finding the average score of a student.

Counting how many days are left until a holiday.

Splitting a bill evenly among friends.

Syntax

Ruby

result = number1 + number2
result = number1 - number2
result = number1 * number2
result = number1 / number2
result = number1 % number2

Use + for addition, - for subtraction, * for multiplication, / for division, and % for remainder (modulus).

Division with / returns a float if any number is a float, otherwise an integer.

Examples

Adds 5 and 3, then prints 8.

Ruby

sum = 5 + 3
puts sum

Subtracts 4 from 10, then prints 6.

Ruby

difference = 10 - 4
puts difference

Multiplies 7 by 6, then prints 42.

Ruby

product = 7 * 6
puts product

Divides 20 by 4, then prints 5.

Ruby

quotient = 20 / 4
puts quotient

Finds remainder when 17 is divided by 5, then prints 2.

Ruby

remainder = 17 % 5
puts remainder

Sample Program

This program asks for two numbers, then shows the result of adding, subtracting, multiplying, dividing, and finding the remainder.

Ruby

puts "Enter first number:"
num1 = gets.chomp.to_i
puts "Enter second number:"
num2 = gets.chomp.to_i

sum = num1 + num2
difference = num1 - num2
product = num1 * num2
quotient = num1 / num2
remainder = num1 % num2

puts "Sum: #{sum}"
puts "Difference: #{difference}"
puts "Product: #{product}"
puts "Quotient: #{quotient}"
puts "Remainder: #{remainder}"

Important Notes

Division by zero will cause an error, so avoid dividing by zero.

Using to_i converts input to whole numbers; for decimals use to_f.

Summary

Arithmetic operators let you do basic math in Ruby.

Use +, -, *, /, and % for addition, subtraction, multiplication, division, and remainder.

Remember to handle division carefully to avoid errors.

Practice

1. Which of the following is the correct symbol for multiplication in Ruby?

easy

A. -

B. *

C. +

D. /

Solution

1. Step 1: Recall basic arithmetic symbols in Ruby

   Ruby uses standard arithmetic symbols: + for addition, - for subtraction, * for multiplication, / for division.

2. Step 2: Identify the multiplication symbol

   The symbol for multiplication is the asterisk (*).

3. Final Answer:

   * -> Option B

4. Quick Check:

   Multiplication = * [OK]

Hint: Remember * means multiply in most languages including Ruby [OK]

Common Mistakes:

• Confusing + with multiplication
• Using / instead of *
• Using - instead of *

2. Which of the following Ruby expressions correctly calculates the remainder of 10 divided by 3?

easy

A. 10 - 3

B. 10 / 3

C. 10 * 3

D. 10 % 3

Solution

1. Step 1: Understand the modulus operator

   The modulus operator (%) returns the remainder after division.

2. Step 2: Identify the correct expression for remainder

   10 % 3 calculates the remainder when 10 is divided by 3, which is 1.

3. Final Answer:

   10 % 3 -> Option D

4. Quick Check:

   Remainder = % [OK]

Hint: Use % to get remainder after division [OK]

Common Mistakes:

• Using / instead of %
• Using * or - which do not give remainder
• Confusing % with division

3. What is the output of the following Ruby code?

result = 15 / 4
puts result

medium

A. 3

B. SyntaxError

C. 4

D. 3.75

Solution

1. Step 1: Understand integer division in Ruby

   When dividing two integers, Ruby performs integer division, discarding the decimal part.

2. Step 2: Calculate 15 divided by 4 as integer division

   15 / 4 equals 3.75, but integer division returns 3.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Integer division truncates decimals = 3 [OK]

Hint: Integer division drops decimals unless floats used [OK]

Common Mistakes:

• Expecting float result without floats
• Confusing / with %
• Thinking output is 4 or 3.75

4. Identify the error in this Ruby code snippet:

num = 10
result = num / 0
puts result

medium

A. Division by zero error

B. Syntax error due to missing operator

C. No error, output is 0

D. Variable 'num' is undefined

Solution

1. Step 1: Analyze the division operation

   The code divides 10 by 0, which is mathematically undefined.

2. Step 2: Understand Ruby's behavior on division by zero

   Ruby raises a ZeroDivisionError when dividing by zero.

3. Final Answer:

   Division by zero error -> Option A

4. Quick Check:

   Dividing by zero causes error [OK]

Hint: Never divide by zero; it causes runtime error [OK]

Common Mistakes:

• Thinking output is 0
• Assuming syntax error
• Ignoring runtime exceptions

5. You want to calculate the average of three numbers: 7, 8, and 9 in Ruby. Which expression correctly computes the average as a float?

hard

A. 7 + 8 + 9 / 3

B. (7 + 8 + 9) / 3

C. (7 + 8 + 9) / 3.0

D. (7 + 8 + 9) % 3

Solution

1. Step 1: Calculate sum of numbers

   Sum is 7 + 8 + 9 = 24.

2. Step 2: Divide by 3 as float division

   Dividing by 3.0 forces float division, giving 8.0 instead of integer 8.

3. Final Answer:

   (7 + 8 + 9) / 3.0 -> Option C

4. Quick Check:

   Use float divisor for float average [OK]

Hint: Divide by float (3.0) to get decimal average [OK]

Common Mistakes:

• Using integer division losing decimals
• Misusing % instead of /
• Wrong operator precedence without parentheses