help with arrays

[droidus]

i am learning about arrays, and have this assignment:

Counts the frequencies of letters A-Za-z in a string
@param str a string
@return an array of 26 counts. The i-th count is the number of occurrences
of 'A' + i or 'a' + i.

and here is my coding so far:

	int[]count = new int[26];
	int counter = 1;
	int number = 0;
	char[]alphabet = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'};
        
        for (int i = 0; i < str.length(); i++) 
		  {
            
				if (Character.isLetter(str.charAt(i)))
				{
					counter++;
					
					
					while (alphabet[i] == str.charAt(i))
					{
						counter++;
					}
					
					
				}
				
			count[i] = counter;
        }

	return count;

i am thinking that i need to update my "i" for both my alphabet array, and the string, charAt.

[sunde887]

What errors are you getting?(if compiler errors copy and paste the exact message, if logical show output and expected output)

Also, be sure to ask specific questions.

[Junky]

You are making this harder than it needs to be. A little hint:

char c = 'a';
String s = "abz";
for(int index = 0; index < s.length(); index++) {
    System.out.println((int) s.charAt(index) - c);
}

[droidus]

ok, so i put in a string, and will get consecutive numbers, such as 2, 3, 5, 6, 6, 7.

and thanks for the quick response!

what is the "- c"? i am confused, because i would think that that would be a number.
i get 0, 1, 25?

[Junky]

what is the "- c"? i am confused, because i would think that that would be a number.
i get 0, 1, 25?

Exactly. For 'a' the result is 0, for 'b' it is 1, for 'c' it is 2, ..... for 'z' it is 25. Do those numbers ring any bells? Array indicies perhaps.

[droidus]

oh, ok... those are just the indexs then. i'll see what i can do with this...

[droidus]

how about this for pseudocode?:

Where
     index number (found from code above) = number of index in array, update counter (+1) for that array slot

[droidus]

got it! here is what i have:

		char c = 'a';
	int test = 0;
	int[]letters = new int[26];
	int counter = 0;
	
	for(int index = 0; index < str.length(); index++) {
   	test = ((int) str.charAt(index) - c);
		letters[test] = letters[test]+1;
	}
	
	for (int index=0; index < 26; index++) {
		System.out.print(letters[index] + ", ");
	}

output (for hello):

0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 2, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

how do i remove the last comma?

[Junky]

Your current algorithm is to print a number followed by a comma, except the last one. The problem is how do you know when you get to the last one.

A better and easier algorithm is to print a comma before the number except the first one.

[droidus]

with

for (int index=0; index < 26; index++) {
	counter++;
		if (counter == 1) {
			System.out.print(letters[index] + ", ");
		}
		else {
			System.out.print(", " + letters[index]);
		}
	}

i get:

0, , 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 2, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

[Junky]

You need to refine the algorithm. You always want to print the number so remove that from the if statement.

loop {
    if not first number {
        print comma
    }
    print number

By the way you can use the loop control variable for this and get rid of the counter.

[droidus]

when i run this, and return letters, i get some weird string. here is my code, and my output:

char c = 'a';
	int test = 0;
	int[]letters = new int[26];
	int counter = 0;
	
	for(int index = 0; index < str.length(); index++) {
   	test = ((int) str.charAt(index) - c); // Gets the string letter position in the alphabet
		letters[test] = letters[test]+1; // Gets the position in the array, and adds one to that index value
	}

[I@3e25a5

what is going on here??

[ivlatt]

I believe that's outputting a memory address (usually because you're not indexing the array correctly)

I'm at work at the moment (so can't look too much in to it), if nobody has responded with a fix before I get home (a couple of hrs) then I'll have a look at it then

[droidus]

it sounds like it's the uppercase "H" for hello. i get an java.lang.ArrayIndexOutOfBoundsException error.

[ivlatt]

it sounds like it's the uppercase "H" for hello. i get an java.lang.ArrayIndexOutOfBoundsException error.

for(int index = 0; index < str.length(); index++)

To do with that perhaps?

.length results the total number of indexes in the array. Although your last index would be .length-1 (remember - because an array starts from position 0)

[JosAH]

for(int index = 0; index < str.length(); index++)

To do with that perhaps?

.length results the total number of indexes in the array. Although your last index would be .length-1 (remember - because an array starts from position 0)

That has nothing to do with it; that simple calculation assumes that the characters are in the range 'a' ... 'z'. If you subtract an 'a' from the character the index value is in the range 0 ... 25. An uppcase character is out of that range so the result is a negative index value which results in an AIOOBE.

kind regards,

Jos

[droidus]

ok. so how would i get around this? would i just have to use a switch statement?

[JosAH]

ok. so how would i get around this? would i just have to use a switch statement?

Nope, a switch statement is so old fashioned; think about it: do you just want statistics (frequencies) of lower case letters? If so, you have to exclude any other character from your input. If not, you either have to use a much larger array (where every possible character can be a index) or abandon the array approach entirely. The choice is up to you.

kind regards,

Jos

[droidus]

i have to return an array, and it can only have 26 values (for each letter).

[Junky]

Convert your String to lowercase.