Upto and downto methods in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers from 1 to 5 using upto method.

Ruby

1.[1](5) { |i| puts i }

Drag options to blanks, or click blank then click option'

Atimes

Bdownto

Cupto

Deach

Attempts:

3 left

💡 Hint

Common Mistakes

Using downto instead of upto will count downwards.

Using times or each will not work directly on a number.

The upto method counts upwards from the starting number to the given number.

2fill in blank

medium

Complete the code to print numbers from 5 down to 1 using downto method.

Ruby

5.[1](1) { |i| puts i }

Drag options to blanks, or click blank then click option'

Adownto

Btimes

Ceach

Dupto

Attempts:

3 left

💡 Hint

Common Mistakes

Using upto instead of downto will count upwards.

Using times or each will not work directly on a number.

The downto method counts downwards from the starting number to the given number.

3fill in blank

hard

Fix the error in the code to print numbers from 3 up to 7.

Ruby

3.[1](7) { |num| puts num }

Drag options to blanks, or click blank then click option'

Aeach

Bupto

Cdownto

Dtimes

Attempts:

3 left

💡 Hint

Common Mistakes

Using downto will not print anything because 3 is less than 7.

Using each or times on a number is incorrect.

To count upwards from 3 to 7, use upto. Using downto would count downwards and cause no output here.

4fill in blank

hard

Fill both blanks to create a hash with keys from 1 to 4 and values counting down from 4 to 1.

Ruby

result = { [1].[2](1) { |i| [i, 5 - i] } }

Drag options to blanks, or click blank then click option'

A1

B4

Cdownto

Dupto

Attempts:

3 left

💡 Hint

Common Mistakes

Using upto instead of downto will count upwards.

Starting from 1 instead of 4 will reverse keys and values.

Start from 4 and count down to 1 using downto. The keys are from 4 down to 1, values calculated as 5 - key.

5fill in blank

hard

Fill all three blanks to create a hash with keys from 'a' to 'c' and values from 1 up to 3.

Ruby

letters = ('a'..'c').to_a
numbers = 1.[1](3).to_a
result = { [2].zip([3]).to_h }

Drag options to blanks, or click blank then click option'

Aupto

Bletters

Cnumbers

Ddownto

Attempts:

3 left

💡 Hint

Common Mistakes

Using downto instead of upto for numbers.

Mixing letters and numbers in wrong order.

Use upto to get numbers from 1 to 3. Then zip letters and numbers arrays to create the hash.

Practice

1. What does the Ruby method 5.upto(8) do?

easy

A. Counts from 5 down to 8, excluding 8

B. Counts from 8 down to 5, including both 8 and 5

C. Counts from 5 up to 8, including both 5 and 8

D. Counts from 8 up to 5, excluding 5

Solution

1. Step 1: Understand the upto method

   The upto method counts upwards from the starting number to the ending number, including both.

2. Step 2: Apply to the example 5.upto(8)

   This means it counts 5, 6, 7, 8 in order.

3. Final Answer:

   Counts from 5 up to 8, including both 5 and 8 -> Option C

4. Quick Check:

   upto counts up = A [OK]

Hint: Remember: upto counts up, downto counts down [OK]

Common Mistakes:

• Confusing upto with downto
• Thinking it excludes the last number
• Assuming it counts down instead of up

2. Which of the following is the correct syntax to count down from 10 to 7 using downto in Ruby?

easy

A. 10.downto(7) { |i| puts i }

B. 10.upto(7) { |i| puts i }

C. 7.downto(10) { |i| puts i }

D. 7.upto(10) { |i| puts i }

Solution

1. Step 1: Identify correct method for counting down

   To count down from 10 to 7, use downto starting at 10 and ending at 7.

2. Step 2: Check syntax correctness

   10.downto(7) { |i| puts i } correctly counts down and prints each number.

3. Final Answer:

   10.downto(7) { |i| puts i } -> Option A

4. Quick Check:

   Count down syntax = C [OK]

Hint: downto starts at bigger number, ends at smaller [OK]

Common Mistakes:

• Using upto instead of downto for counting down
• Reversing start and end numbers
• Missing the block syntax

3. What is the output of this Ruby code?

sum = 0
3.upto(5) { |i| sum += i }
puts sum

medium

A. 12

B. 15

C. 9

D. Error

Solution

1. Step 1: Understand the loop range

   3.upto(5) iterates over 3, 4, 5.

2. Step 2: Calculate sum of values

   sum = 0 + 3 + 4 + 5 = 12.

3. Final Answer:

   12 -> Option A

4. Quick Check:

   3 + 4 + 5 = 12 [OK]

Hint: Add all numbers from start to end inclusive [OK]

Common Mistakes:

• Adding only start and end numbers
• Confusing upto with downto
• Forgetting to include the last number

4. Identify the error in this Ruby code:

5.upto(3) { |i| puts i }

medium

A. Syntax error due to wrong method usage

B. No output because start is greater than end

C. Infinite loop occurs

D. Outputs numbers from 5 down to 3

Solution

1. Step 1: Analyze the upto method behavior

   upto counts up from start to end. Here start=5, end=3, which is invalid for counting up.

2. Step 2: Determine output

   Since 5 is already greater than 3, the block does not run and no output is produced.

3. Final Answer:

   No output because start is greater than end -> Option B

4. Quick Check:

   upto with start > end = no output [OK]

Hint: upto does nothing if start > end, no error [OK]

Common Mistakes:

• Expecting output when start > end
• Thinking it counts down automatically
• Assuming syntax error occurs

5. Using downto, how can you create an array of even numbers counting down from 10 to 2?

hard

A. arr = []
2.upto(10) { |i| arr << i if i.even? }

B. arr = []
2.downto(10) { |i| arr << i if i.even? }

C. arr = []
10.upto(2) { |i| arr << i if i.even? }

D. arr = []
10.downto(2) { |i| arr << i if i.even? }

Solution

1. Step 1: Choose correct method for counting down

   To count down from 10 to 2, use downto starting at 10 and ending at 2.

2. Step 2: Filter even numbers inside the block

   Use if i.even? to add only even numbers to the array.

3. Final Answer:

   arr = [] 10.downto(2) { |i| arr << i if i.even? } -> Option D

4. Quick Check:

   downto + even check = B [OK]

Hint: Use downto with condition inside block to filter [OK]

Common Mistakes:

• Using upto instead of downto for counting down
• Reversing start and end numbers
• Not filtering even numbers correctly