trim and pad

Learn formatting with trim, padLeft and padRight.

trim

To remove the whitespace characters (space, tab, newline) at the start and end of a string use trim. It is especially useful when taking user input; if the user accidentally left a space you clean it up. " apple ".trim() gives "apple".

If you only want to clean one side, there are trimLeft and trimRight as well. trim does not modify the original string; it returns a new one. So do not forget to assign the result to a variable.

padLeft and padRight

To pad a string to a given length use padLeft and padRight. They fill the missing characters with a character you choose. "7".padLeft(3, "0") gives "007". Ideal for showing numbers at a fixed width.

If no padding character is given, space is used by default. padRight does the same from the right: "ad".padRight(5, "_") gives "ad___". Neither adds anything if the string already meets or exceeds the target length; they never shorten it.

Exercise Your turn: trim and padLeft

First trim the string " 7 ", then pad it to three characters on the left with padLeft(3, "0"). Print the result with print.

Show example solution

void main() {
  final result = "  7  ".trim().padLeft(3, "0");
  print(result);
}

Test yourself

What does " apple ".trim() return?
```
final x = "  apple  ".trim();
```
- "apple "
- "apple"
- " apple"
- " apple "
Show answer

" apple" — trim cuts spaces from both sides.

The trim call

final clean = "  apple  ".____();

Show answer

final clean = "  apple  ".trim();

Match trim and pad

trim

cuts spaces on both sides
trimLeft

cuts spaces on the left
padLeft

pads on the left
padRight

pads on the right

Next lesson: RegExp

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