Change int to string in a matrix

Question

I want to convert some integers into a * based on a rule. I can determine which places in the matrix it should convert, but cannot convert it. I give the program the first matrix and it should return the second matrix:

my code is this:

for(int i=1; i<r-1; i++) {
  for(int a=1; a<c-1; a++){
    if(matrix[i-1][a] < matrix[r][a] && matrix[i+1][a] < matrix[r][a] && matrix[i][a-1] < matrix[r][a] && 
       matrix[i][a+1] < matrix[r][a]) {
      matrix[r][a] = *;
    }
  }
}

Edit: The matrix is an int type. I can determine which locations in the matrix should be converted, however the convertion itself does not work.

I get this error: Error: Syntax error on token "*", invalid Expression

i have some other code that determine the position in the matrix that should be converted. But the convertion itself does not work. — T.v.L., May 03 '18 at 20:27
If the matrix store `int` values, you can't store string or char values. So first you need to store those numbers in a string matrix and then change them to `*`. — CryogenicNeo, May 03 '18 at 20:30
What "*does not work*" mean? Do you get a compile-time error? An `Exception`? Unexpected behaviour? Please be precise. — Turing85, May 03 '18 at 20:30
@CryogenicNeo "*If the matrix store int values, you can't store string or char values.*" - That is only partly true. `char`s can be widened to `int`. — Turing85, May 03 '18 at 20:30
Yes, that's true, but it's useless in this case because if you would convert integers into chars by their value, will be cases that values or number are replaced with `*`. — CryogenicNeo, May 03 '18 at 20:34
Do you get an `Exception` or an `Error`? Please [edit] your question and add the stack trace. It would also be beneficial if you mark the line throwing the `Exception`/`Error`. — Turing85, May 03 '18 at 20:34
@Turing85 I edited my question. It looks like an error from my compiler, but i do not have much experience. — T.v.L., May 03 '18 at 20:37
Okay, I see the problem. You should revisit some basic tutorials like [this one by Oracle](https://docs.oracle.com/javase/tutorial/java/nutsandbolts/index.html) and familiarize yourself with primitive types and how to work with them. — Turing85, May 03 '18 at 20:40
@Turing85 I understand that * is not an integer. I also tried .equals but that did not work too. Could I convert the whole matrix first to an string type and then replace some field with *? — T.v.L., May 03 '18 at 20:55
You can, yes. But you would have to create a `String[][]` and copy each value manually. — Turing85, May 03 '18 at 20:57
@Turing85 Okay thanks, I am going to try that. Or do you have a faster solution? (Maybe start with an string matrix) — T.v.L., May 03 '18 at 21:00
Experiment yourself. Programming is a craft, the more you do it, the better you become. — Turing85, May 03 '18 at 21:02

Oleg Cherednik · Answer 1 · 2018-05-03T20:41:21.700

You could leave int[][] matrix, and e.g. mark a * cells with some illegal number (e.g. Integer.MAX_VALUE). And when you print or use this matrix, do like: System.out.print(matrix[i][k] != Integer.MAX_VALUE ? matrix[i][k] : '*')

public static void main(String... args) {
    int[][] matrix = new int[5][5];
    modifyMatrix(matrix);
    print(matrix);
}

public static void modifyMatrix(int[][] matrix) {
    for (int row = 0; row < matrix.length; row++)
        for (int col = 0; col < matrix[row].length; col++)
            if (isStar(row, col, matrix))
                matrix[row][col] = Integer.MAX_VALUE;
}

private static boolean isStar(int row, int col, int[][] matrix) {
    // TODO your condition to place a '*'
    return false;
}

private static void print(int[][] matrix) {
    for (int row = 0; row < matrix.length; row++) {
        for (int col = 0, max = matrix[row].length; col < msx; col++) {
            System.out.print(matrix[row][col] != Integer.MAX_VALUE ? matrix[row][col] : '*');
            System.out.println(col != max - 1 ? ' ' : '\0');
        }
        System.out.println();
    }
}

score 1 · Answer 2 · answered May 03 '18 at 20:35

1

you can use matrix of type Integer instead of int and then mark a * cell with null

Then when printing or using matrix show null values with *

answered May 03 '18 at 20:35

ygngy

3,630
2
18
29

[What could possibly go wrong?](https://384uqqh5pka2ma24ild282mv-wpengine.netdna-ssl.com/wp-content/uploads/2016/06/Top10Exceptions-1.png) – Turing85 May 03 '18 at 20:38
1

@Turing85 with a simple `if` the `null` value could be checked. the benefit of `null` value is that it is always invalid value you may need any other supposed invalid value in the future such as `Integer.MAX_VALUE` or others – ygngy May 03 '18 at 20:41
I prefer to use `int` instead of `Integer` where is is possible – Oleg Cherednik May 03 '18 at 20:41
Of course. That is true for ever `null`. Yet, the `NPE` is the most prominent exception and there are languages, like Kotlin, explicitly trying to add `null`-safety. – Turing85 May 03 '18 at 20:42

score 0 · Answer 3 · answered May 03 '18 at 21:12

0

In an int matrix you can't put characters or symbols(like '*')

The easiest thing to do is to change the type of the matrix. You should use char instead of int.

  char[][] matrix = new char[r][c];

If you want to use an element from the matrix for equations you can use the

Character.getNumericValue(matrix[i][j]);

With this code it will return the number and if it has not numeric value it will return -1

You can check this link for the getNumericValue click here

answered May 03 '18 at 21:12

Mike Bean

3
5

And what if we want **numbers with more than one digit**? for example `23` this is two characters or `789` is three characters so we have to use `String` instead of `char` – ygngy May 04 '18 at 10:26
The example that he gave us is only a digit. if he wants to use more than one characters he can use **String[][]** but he has to change a little the code. Instead of Character.getNumericValue(matrix[i][j]); he can use a for(int k =0; i – Mike Bean May 07 '18 at 11:21

score 0 · Answer 4 · answered May 03 '18 at 21:54

you should create an new array of strings the size of your matrix.

then run trough your matrix and either add the number or change it into a string, like this:

public String[] convert(int[] matrix,int rule) {
    String[][] arr = new String[matrix.length][matrix[0].length];
    for(int i = 0;i<matrix.length;i++) {
        for(int j = 0; j<matrix[i].length;j++) {
            if(matrix[i][j] == rule)
                arr[i][j] = "*";
            else
               arr[i][j] = String.valueOf(matrix[i][j]);
    return arr;

Change int to string in a matrix

4 Answers4