Java reading .txt file to array

Question

I've been trying to workout this excersise all day, but not having any luck. Thanks in advance for any help.

Here's the problem

The approach you are to implement is to store each integer in an array of digits, with one digit per array element. We will be using arrays of length 50, so we will be able to store integers up to 50 digits long. We have to be careful in how we store these digits. Consider, for example, storing the numbers 38423 and 27. If we store these at the “front” of the array with the leading digit of each number in index 0 of the array, then when we go to add these numbers together, we're likely to add them like this:

38423

27

To simulate this right-shifting of values, we will store each value as a sequence of exactly 50 digits, but we'll allow the number to have leading 0's. For example, the problem above is converted into:

0000000000000000000038423

0000000000000000000000027

Now the columns line up properly and we have plenty of space at the front in case we have even longer numbers to add to these.

The data for your program will be stored in a file called sum.txt. Each line of the input file will have a different addition problem for you to solve. Each line will have one or more integers to be added together. Take a look at the input file at the end of this write-up and the output you are supposed to produce. Notice that you produce a line of output for each input line showing the addition problem you are solving and its answer. Your output should also indicate at the end how many lines of input were processed. You must exactly reproduce this output.

You should use the techniques described in chapter 6 to open a file, to read it line by line, and to process the contents of each line. In reading these numbers, you won't be able to read them as ints or longs because many of them are too large to be stored in an int or long. So you'll have to read them as String values using calls on the method next(). Your first task, then, will be to convert a String of digits into an array of 50 digits. As described above, you'll want to shift the number to the right and include leading 0's in front. The String method charAt and the method Character.getNumericValue will be helpful for solving this part of the problem.

You are to add up each line of numbers, which means that you'll have to write some code that allows you to add together two of these numbers or to add one of them to another. This is something you learned in Elementary School to add starting from the right, keeping track of whether there is a digit to carry from one column to the next. Your challenge here is to take a process that you are familiar with and to write code that performs the corresponding task.

Your program also must write out these numbers. In doing so, it should not print any leading 0's. Even though it is convenient to store the number internally with leading 0's, a person reading your output would rather see these numbers without any leading 0's.

You can assume that the input file has numbers that have 50 or fewer digits and that the answer is always 50 digits or fewer. Notice, however, that you have to deal with the possibility that an individual number might be 0 or the answer might be 0. There will be no negative integers in the input file.

You should solve this problem using arrays that are exactly 50 digits long. Certain bugs can be solved by stretching the array to something like 51 digits, but it shouldn't be necessary to do that and you would lose style points if your arrays require more than 50 digits.

The choice of 50 for the number of digits is arbitrary (a magic number), so you should introduce a class constant that you use throughout that would make it easy to modify your code to operate with a different number of digits.

Consider the input file as an example of the kind of problems your program must solve. We might use a more complex input file for actual grading.

The Java class libraries include classes called BigInteger and BigDecimal that use a strategy similar to what we are asking you to implement in this program. You are not allowed to solve this problem using BigInteger or BigDecimal. You must solve it using arrays of digits.

Your program should be stored in a file called Sum.java.

Input file sum.txt

82384
204 435
22 31 12
999 483
28350 28345 39823 95689 234856 3482 55328 934803
7849323789 22398496 8940 32489 859320
729348690234239 542890432323 534322343298
3948692348692348693486235 5834938349234856234863423
999999999999999999999999 432432 58903 34
82934 49802390432 8554389 4789432789 0 48372934287
0
0 0 0
7482343 0 4879023 0 8943242
3333333333 4723 3333333333 6642 3333333333

Output that should be produced

82384 = 82384
204 + 435 = 639
22 + 31 + 12 = 65
999 + 483 = 1482
28350 + 28345 + 39823 + 95689 + 234856 + 3482 + 55328 + 934803 = 1420676
7849323789 + 22398496 + 8940 + 32489 + 859320 = 7872623034
729348690234239 + 542890432323 + 534322343298 = 730425903009860
3948692348692348693486235 + 5834938349234856234863423 = 9783630697927204928349658
999999999999999999999999 + 432432 + 58903 + 34 = 1000000000000000000491368
82934 + 49802390432 + 8554389 + 4789432789 + 0 + 48372934287 = 102973394831
0 = 0
0 + 0 + 0 = 0
7482343 + 0 + 4879023 + 0 + 8943242 = 21304608
3333333333 + 4723 + 3333333333 + 6642 + 3333333333 = 10000011364

Total lines = 14

My code thus far

public class Sum {

    public static void main(String args[]) throws FileNotFoundException{
        File file = new File("sum.txt");
        Scanner scanner = new Scanner(file);
        String[] myInts = new String[50];
        int mySpot = 0;
        while(scanner.hasNext()){
            myInts[mySpot] = scanner.next();
            mySpot++;
        }
        for(int i = 0; i < myInts.length; i++){    
        }
        System.out.println(Character.getNumericValue(myInts[0]));
        System.out.println(Arrays.toString(myInts));
    }
}

Answer 1

When all else fails read the instructions:

"The approach you are to implement is to store each integer in an array of digits, with one digit per array element. We will be using arrays of length 50, so we will be able to store integers up to 50 digits long."

Tells me that this line:

String[] myInts = new String[50];

Has some significant problems.

Tip 1: Don't call it myInts when it's an array of String objects. Things are hard enough already.

Tip 2: Understand that new String[50] is not going to give you a string sized to 50 characters. It's going to give you space to store references to 50 string objects.

Tip 3: Understand that each line of your input can be solved separately so there is no need to remember anything from the lines you've solved before.

Tip 4: Read one line at a time into String line;

Tip 5: After reading a line solve the display problem in two parts: left side and right side of ='s.

Tip 6: Left side: display the line with spaces replaced with space + space. line.replace(" "," + ");

Tip 7: Right side: use line.split(" ") to split line on space, loop the split array of strings, each of these strings is what you'll be converting to int arrays.

Tip 8: "convert a String of digits into an array of 50 digits" <- Life will be easier if you write a method that does this. Take a String. Return an int[]. private int[] makeIntArray(String num) Take care of the "right shifting/leading zero" problem here.

Tip 9: int and long aren't big enough to hold the bigger numbers so break the number String down to Strings of digits before converting to int[].

Tip 10: Read Splitting words into letters in Java

Tip 11: Read Split string into array of character strings

Tip 12: Once you have single characters you can use Integer.parseInt(singleCharString[index--]) if you broke it down to an array of strings or Character.digit( chr[index--], 10); if you broke it down to an array of characters.

Tip 13: "write some code that allows you to add together two of these numbers or to add one of them to another." Read that carefully and it tells you that you really need to declare two vars. int[] sum = new sum[SIZE]; and int[] next = new next[SIZE]; where size is private final static int SIZE = 50;

Tip 14: adding two of these int[] numbers to produce a new int[] would be another good time to make a method. int[] sum(int[] op1, int[] op2)

Tip 15: Since all our int[]'s are right shifted already and always 50 long start a loop with i at 49 and count down. result[i-1] = (op1[i] + op2[i] + carry) % 10; and carry = (op1[i] + op2[i] + carry) / 10 will come in handy. Make sure to stop the loop at 1 or [i-1] will go index out of bounds on you.

Tip 16: Test, Test, and Test again. Make small changes then test. Small change, test. Don't just type and pray. Use the debugger if you like but personally I prefer to check values like this System.out.println("line: " + line);//TODO remove debugging code

Answer 2

Tip #1 : Initialize the array with 0. That way, when you process the file, all you have to worry about is to replace the index locations with the digits obtained from your file.

Tip #2 : You have to do some repeated division by 10 and modulus operation to extract the digits from the number (or binary shift if you prefer). For example, to split the the digits from '27', you can do 27 % 10 (7) and 27 / 10 (2). The key here is to store the result as int . After all, each digit is a whole number (not a floating point number). For number of greater magnitude, you will need to discard the process digit position so that the number gets smaller. You will now when you are done when the quotient of the division is equal to zero. Therefore, you can say in pseudo-code: DIVIDE number by 10 WHILE number > 0 (something like that)

Tip #3 , you will have to iterate in reverse to store the digits in the array. If the array has a length of 50, you will start with LENGTH-1 and count down to ZER0.

Tip #4 : Use an array of ints not an array of Strings if the problem allows you to. Use Integer.parseInt(String s) to convert the numeric String to a primitive int .

Answer 3

I think the question says to read each digit into a different array of standard size while you are reading all the words into a same a same array. and it will also be good to process this line by line

something like this

  Scanner scanner = new Scanner(file);
    int[][] myInts = new int[wordSize][];
    int mySpot = 0;
    while (scanner.hasNextLine()) {
        Scanner scanner1 = new Scanner(scanner.nextLine());
        while (scanner1.hasNext()) {
            String s = scanner1.next();

            int i;
            for ( i= 0; i < wordSize - s.length(); i++) {
                myInts[i][mySpot] = 0;
            }
             i--;
            for (int j=0;j < s.length(); i++,j++) {
                myInts[i][mySpot] = Character.digit(s.charAt(i), 10);
            } 
            mySpot++;
        }

        // do the additions here and add this line to output file  
    }