Arithmetic operators in Ruby - Step-by-Step Execution

Concept Flow - Arithmetic operators

Start

↓

Read operands

↓

Choose operator (+, -, *, /, %)

↓

Perform calculation

↓

Store/Display result

↓

End

This flow shows how Ruby reads two numbers, applies an arithmetic operator, calculates the result, and then shows it.

Execution Sample

Ruby

a = 10
b = 3
sum = a + b
product = a * b
remainder = a % b

This code adds, multiplies, and finds the remainder of two numbers.

Execution Table

Step	Variable	Operation	Operands	Result
1	a	Assign	10	10
2	b	Assign	3	3
3	sum	Addition (+)	10 + 3	13
4	product	Multiplication (*)	10 * 3	30
5	remainder	Modulo (%)	10 % 3	1

💡 All operations completed, variables hold their calculated values.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5
a	nil	10	10	10	10	10
b	nil	nil	3	3	3	3
sum	nil	nil	nil	13	13	13
product	nil	nil	nil	nil	30	30
remainder	nil	nil	nil	nil	nil	1

Key Moments - 2 Insights

Why does the remainder operator (%) give 1 when dividing 10 by 3?

Because 10 divided by 3 is 3 with a remainder of 1, as shown in step 5 of the execution_table.

Why do variables keep their values after each operation?

Each assignment stores the result in the variable, so after step 3, 'sum' holds 13, and it stays until changed.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'product' after step 4?

A 1

B 13

C 30

D 3

💡 Hint

Check the 'Result' column for 'product' at step 4 in the execution_table.

At which step is the addition operation performed?

A Step 3

B Step 2

C Step 4

D Step 5

💡 Hint

Look for the 'Addition (+)' operation in the 'Operation' column of the execution_table.

If 'b' was changed to 5, what would be the new value of 'remainder' at step 5?

A 2

B 0

C 1

D 3

💡 Hint

Calculate 10 % 5 and check the 'remainder' value logic in the variable_tracker.

Concept Snapshot

Ruby arithmetic operators:
+ addition
- subtraction
* multiplication
/ division
% modulo (remainder)
Use variables to store results.

Full Transcript

This visual trace shows how Ruby uses arithmetic operators to calculate values step-by-step. Variables 'a' and 'b' are assigned 10 and 3. Then 'sum' is calculated as a + b = 13. 'product' is a * b = 30. 'remainder' is a % b = 1. Each step updates variables, storing results for later use. The modulo operator (%) gives the remainder after division. This helps beginners see how each operator works and how variables change.

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