'% 02d' What is the percentage of% 2?

'%02d' % 2

When you want to write the number 2 as '02' in ruby, you write a syntax like '% 02d'% 2. The method is to pad the argument with 0 and return it as a string, but what exactly is%, 02, or d here?

% What?

In ruby, the notation% has various meanings.

  1. "%" for remainder Example: 5% 3 => 2
  2. String class "%" operator Example:"% 02d "% 2 =>" 02 "
  3. Literal notation "%" operator Example:% w (dog cat monkey) => ["dog", "cat", "monkey"]
  4. Show input to the command line Example:% x [DATE] =>" Wednesday, June 24, 2020 09:31:57 JST \ n "

There are the above types. Reference: Meanings of symbols used in Ruby (excluding complex symbols in regular expressions)

The syntax '% 02d'% 2 shown above is equivalent to the 2. String class "%" operator in the above example!

What exactly is 02 or d?

d is one of the ** "indicators" ** that indicate the type of the argument. d represents a decimal number (Decimal number). Other directives include those that represent strings, those that represent floating point numbers, and those that represent exponential notation.

02 can be decomposed into 0 and 2, indicating ** "flag" ** and ** "width" **, respectively. There are several types of ** "flags" **, but 0 means to fill the margins with 0s. ** "Width" ** is left as it is, and the length at the time of output is specified.

To summarize these, the notation '% 02d'% 2 is

'% 0 (Please fill the margin with 0 ~) 2 (The length at the time of output is 2) d (Represent the argument as a decimal integer'% (% operator of String class Yo ~) 2 (The argument is 2!)

It means that it has the meaning.

in conclusion

Arguments can also be passed as an array, so ** When you say "I want to convert a decimal color code to a hexadecimal color code" ** You can write '% 02x% 02x% 02x'% [255, 255, 255] =>" ffffff "!

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