When writing large numbers on paper, it’s common to use commas to make the number easier to understand. For example, you could write
Of course, such a number can be hard to read so when writing such large numbers on paper, people use commas to separate every three digits like this:
If you need to use large numbers in a Swift program, you can’t use commas since the computer won’t recognize commas as place markers. Instead, Swift lets you use the underscore character. So if you wanted to declare a variable like this:
var distance = 308945025
You could use an underscore character in place of commas like this:
var distance = 308_945_025
Using the underscore character in large numbers is optional but can make numbers easier for people to read. Remember, given a choice between making programs easier for machines or human beings, always choose to make life easier for people.