Answer 1

In your code you initialize the scanner object as

Scanner sc = sc. new Scanner(System.in);

Should be

Scanner sc = new Scanner(System.in);

Your code also tries to initialize the Scanner object again.

Answer 2

So you have two elements at index a and b in your array and you want to swap values. Use a temporary variable c. Save the contents of the array at index a to variable c. Then replace the content of the array at index a with the contents of the array at index b. Then replace the contents of the array at index b with temporary variable c. All done!