PHP Compiler Testing
Repeating Letters

Create a function that takes a string and returns a string in which each character is repeated once.

Examples

double_char("String") ➞ "SSttrriinngg"

 

double_char("Hello World!") ➞ "HHeelllloo  WWoorrlldd!!"

 

double_char("1234!_ ") ➞ "11223344!!__  "