Luhn Algorithm Computer Code---checking to see if credit card #'s are valid..?

Array d of ints contains the digits of a credit card number, including the check digit in last place. Complete the following code to check (using the Luhn algorithm) whether the credit card number is valid, storing true in valid if and only if it is.

The for-loop in the following code deals with the digits in left-to-right order. Notice, however, that the digit with index i occupies right-to-left position d.length - i. For example, the last digit (which has index d.length - 1) is in right-to-left position

d.length - (d.length - 1) = 1,

and the first digit (which has index 0) is in right-to-left position

d.length - 0 = d.length.

// Enter values to test here

int[] d = { };

boolean valid;

int sum = 0;

int dd;

for ( int i = 0; i < d.length; i++ )

{

// Is right-to-left position even?

if ( /* Your code here */ )

{

// If it is, set dd to twice the digit

dd = /* Your code here */ ;

// Add the sum of dd's digits to sum

sum += /* Your code here */ ;

}

else

{

// If right-to-left position is odd,

// add the digit to sum

sum += /* Your code here */ ;

}

}

valid = /* Your code here */ ;