length and methods

Learn .length and String methods.

length and methods

You find how many characters a String has with the .length property: "Welcome".length evaluates to 7. .length is a property, not a method; no parentheses needed.

To upper-case the letters you use .toUpperCase(), to lower-case them .toLowerCase(). For example "book".toUpperCase() returns "BOOK". These methods do not change the original string; they return a new one.

Methods return a new string

Important: .toUpperCase() and .toLowerCase() do not modify the original string. String name = "Alex"; name.toUpperCase(); produces a new string "ALEX" but name stays "Alex".

To keep the result you assign it to a new variable: String big = name.toUpperCase();. Now big is "ALEX" and name is "Alex". Strings in Dart are immutable; every method call creates a new string.

Exercise Upper-case the city

Declare a String variable city with the value "Paris". Declare a new variable big and assign the result of city.toUpperCase() to it. Then print big with print(big);. The output on a single line must be PARIS.

Show example solution

String city = "Paris";
var big = city.toUpperCase();
print(big);

Test yourself

Write the length call

String word = "Welcome";
print(word____);

Show answer

String word = "Welcome";
print(word.length);

What does "book".toUpperCase() return?
```
"book".toUpperCase()
```
- "book"
- "Book"
- "BOOK"
- true
Show answer

"BOOK" — toUpperCase upper-cases all letters: BOOK.
Match each method to its job

.length

Character count
.toUpperCase()

Upper-cases letters
.toLowerCase()

Lower-cases letters
print(x)

Prints to screen

Next lesson: substring

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