where do i put local variables in Dart code code example

Example 1: dart ?? operator

int val1;
final int val2 = 20;

console.log(val1 ?? val2); //result => 20 because val1 is null

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final int val1 = 30;
final int val2 = 20;

console.log(val1 ?? val2); //result => 30 because val1 is not null

Example 2: dart function syntax

sum(x, y) {
	return x + y;
}

// This is where the app starts executing.
void main() {
  print(sum(3,5)); // => 8
}