Need to fix for loop

Yo, the thing is deeper than one might think. I always found these loop over character examples nasty, i got it at my last job interview. So here we go:

If the exercise would be this way: rows got from 1..n, columns for 1..n, output should be "1/1, 1/2...3/1, 3/2...", it would be straight forward, wouldn't it?

public void seatnumbersNumbersOnly() {
        int numRows = 3;
        int numColumns = 3;

        for (int currentRow = 1; currentRow <= numRows; currentRow++) {
            for (int currentColumn = 1; currentColumn < numColumns; currentColumn++) {
                System.out.print(currentColumn + "/" + currentRow + " ");
            }
        }
    }

But the task is different, they want letters for the columns. Let's brute force it on the same basis.

public void seatnumbersNumbersMappedAgain() {
String[] seatLetters = new String []{"A", "B", "C"}; // so many letters as there are columns. Note: array index is 0-based
int numRows = 3;
int numColumns = 3;

for (int currentRow = 1; currentRow <= numRows; currentRow++) {
    for (int currentColumn = 1; currentColumn < numColumns; currentColumn++) {
        // seatLetters[i] is a string "s", not a char 'c', so everything's fine
        System.out.print(seatLetters[currentColumn - 1] + currentRow + " "); // -1: seatLetters indexing is zero based
    }
}

}

But then: in Java char and byte are interchangeable as long as you're in the ascii-range, you can assign a char literal to a byte and the other way round.

@Test
public void charByteEquivalence() {
    // check out http://www.asciitable.com/
    char ca = 'A';
    byte ba = 0x41;
    assertEquals(ca, ba);

    ca = 0x41;
    ba = 'A';
    assertEquals(ca, ba);
}

This means, you also can use the char variable directly for looping. But watch out, building the output string becomes messy, since you have to watch what gets "+"ed with what. You want String/char values for columns and numbers for rows. A "string" + char/byte/int ... becomes a string. char + int becomes and int? a byte? a char? Just certainly not a String. Disclosure: I trial-and-errored the string concatenation, and it becomes an int. Some examples for implicit type conversions are here, the official reference is here.

    public void seatnumbersChar() {
    int numRows = 3;
    int numColumns = 3;

    char firstColumnLetter = 'A';
    for (int currentRow = 1; currentRow <= numRows; currentRow++) {
        for (char currentColumn = firstColumnLetter; currentColumn < firstColumnLetter + numColumns; currentColumn++) {
            // at this point you have to watch out currentColumn + currentRow + " " will get evaluated left to right

            // currentRow is an int
            // currentColumn becomes an int when "+"ed with currentRow 
            // so currentRow + currentColumn would add two numbers instead of concatenating 2 strings, therefore
            // an explicit conversion to string is needed for one of the arguments
            System.out.print(currentColumn + String.valueOf(currentRow) + " ");
        }
    }
}

The same example going the byte route, similar mess with string concatenation, but not quite the same.

public void seatnumbersByte() {
    int numRows = 3;
    int numColumns = 3;

    byte firstColumnLetter = 'A';
    for (int currentRow = 1; currentRow <= numRows; currentRow++) {
        for (byte currentColumn = firstColumnLetter; currentColumn < firstColumnLetter + numColumns; currentColumn++) {
            // same case other trick: (currentRow + " ") forces the result to be a string due to the + " "
            // currentColumn here is declared as byte, when concatenated to a string the numeric representation would be taken (wtf...?)
            // therefore a cast to char is needed "(char) currentColumn"
            // what's left now ? (currentRow + " ") is a string
            // "(char) currentColumn" is a char
            // a char "+" a string is a string
            System.out.print((char) currentColumn + (currentRow + " "));
        }
    }
}

Hope I got my revenge on that last interview. Have gotten the job anyway ;)

You need to increment the currentColumnLetter inside the inner loop. Remember for each row, you need to traverse each column. That's the reason you are nesting loops, right?

Try this:

for (currentRow = 1; currentRow <= numRows; currentRow++) {
    currentColumnLetter = 'A';
    for (currentColumn = 1; currentColumn <= numColumns; currentColumn++) {
        System.out.print(currentRow);
        System.out.print(currentColumnLetter + " "); 
        currentColumnLetter++ 
    }
}

You do not need this condition in the outer loop:

if( currentColumn == numColumns)
{
    currentColumnLetter++;
}