Ruby How to Convert String to Uppercase Easily

In Ruby, you can convert a string to uppercase by calling the upcase method on the string, like "hello".upcase which returns "HELLO".

Examples

Input"hello"

Output"HELLO"

Input"Ruby Programming"

Output"RUBY PROGRAMMING"

Input"123abc!"

Output"123ABC!"

How to Think About It

To convert a string to uppercase, think of changing every lowercase letter to its uppercase version while leaving other characters unchanged. Ruby provides a simple method called upcase that does this for you automatically.

Algorithm

1

Take the input string.

2

For each character in the string, check if it is a lowercase letter.

3

If it is lowercase, convert it to uppercase.

4

Leave all other characters as they are.

5

Return the new string with all letters in uppercase.

Code

ruby

str = "hello world"
puts str.upcase

Output

HELLO WORLD

Dry Run

Let's trace "hello" through the code

1

Input string

"hello"

2

Call upcase method

"hello".upcase

3

Output string

"HELLO"

Original	After upcase
hello	HELLO

Why This Works

Step 1: What upcase does

The upcase method converts all lowercase letters in the string to uppercase letters.

Step 2: Non-letter characters

Characters that are not letters, like numbers or symbols, remain unchanged by upcase.

Step 3: Returns new string

upcase returns a new string with uppercase letters and does not modify the original string unless you use upcase!.

Alternative Approaches

upcase!

ruby

str = "hello"
str.upcase!
puts str

This method changes the original string in place instead of returning a new one.

tr method

ruby

str = "hello"
puts str.tr('a-z', 'A-Z')

This replaces lowercase letters with uppercase manually but is less readable than upcase.

Complexity: O(n) time, O(n) space

Time Complexity

The method processes each character once, so time grows linearly with string length.

Space Complexity

A new string is created to hold the uppercase result, so space also grows linearly.

Which Approach is Fastest?

upcase is optimized and clear; alternatives like tr are less readable and not faster.

Approach	Time	Space	Best For
upcase	O(n)	O(n)	Simple and clear uppercase conversion
upcase!	O(n)	O(1)	In-place modification to save memory
tr('a-z', 'A-Z')	O(n)	O(n)	Manual replacement, less readable