CODEWITHSUNDEEP
javacharlong-integer
Akhilesh
Akhilesh

Reputation: 47

Unexpected value of Long variable after converting to char array

1. long number = 564; 2. String str = number+""; 3. char[] num = str.toCharArray(); 4. number = number - num[0]; /* The value of number is 511 */

I am trying to subtract the first digit of the number from the number using this piece of code.

During debugging, i found out that the value of num[0] was 53. Can anyone explain what am i missing here.

Upvotes: 0

Views: 148

Answers (3)

sestus
sestus

Reputation: 1927

It just feels wrong to convert a number to a string, extract the first char, convert back to number and subtract. Why don't you extract the first digit while working with numbers directly. Something like this would do:

    long number = 564;

    int digits = 0;
    assert (number > 0);
    for (long num = number; num > 1; num = num / 10 ) {
        digits += 1;
    }
    int firstDigit = (int) (number / Math.pow(10, digits -1));

    number = number - firstDigit;
    System.out.println(number);

If you want to get all digits:

    long number = 564;

    int digits = 0;
    assert (number > 0);
    for (long num = number; num > 1; num = num / 10 ) {
        digits += 1;
    }

    for (int digit = digits - 1; digit >= 0; digit--) {
        int currentDigit = (int) (number / Math.pow(10, digit)) % 10;
        System.out.println(currentDigit);
    }

Upvotes: 0

Mallikarjun Pasunkili
Mallikarjun Pasunkili

Reputation: 271

When you are using the binary operator "-" the smaller datatype, in this case char, is promoted to long which returns the ASCII value of num[0] ('5') which is 53. To get the actual face value of num[0] convert it to String and parse it to Long as Sweeper has pointed out.

Upvotes: 1

Sweeper
Sweeper

Reputation: 271945

I would suggest you to change your fourth line to this:

number = number - Long.parseLong(Character.toString(num[0]));

Basically, what is happening here is that I first convert the char (num[0]) to a string, then parsed the string to a long.

ALternatively, you don't even need to convert the string to a char array! Use charAt() to get the char:

number = number - Long.parseLong(Character.toString(str.charAt(0)));

Upvotes: 1

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