Bao Truong

I'm sorry for the late reply. So it seems we're good, and thanks to this I now know about BigDecimal. Really appreciate it guys.

This is my method to determine if a number is a square number, it is to solve a Kata over at Codewars
public static boolean isSquare(int n) {                if (Math.sqrt(n) == (long)Math.sqrt(n))            return true;        return false;    }
I submitted it and it passed all the test. But will there be some number whose square root's fraction part (the digits after the decimal point) is too small for even the double floating-point number to represent (for example 123.0000000000000000000000000000000000000000000000000000123123 with 52 zeros) so the square root will be seen as an integer and the method will return true while it is actually supposed to return false?
                                                                                                                                                                                                                                                                                                                             

Here's the first method with some changes and the method with no substring()

public int countHiWithSubString(String str) {        int count = 0;        if (str.indexOf("hi") == -1)            return count;        else {            for (int i = 0; i < str.length();) {                int k = str.substring(i).indexOf("hi");                if (k != -1) {                    i += ++k;                    count++;                }                else                    break;            }  // for            return count;        }  // 1st else    }    public int countHi(String str) {        int count = 0;        for (int i = 0; i < str.length() - 1; i++) {            String test = "" + str.charAt(i) + str.charAt(++i);            if (str.length() < 2)                break;            else if (test.equals("hi"))                count++;        }        return count;    }

Thanks guys, I fixed the problem and made a less bulky version without using substring()

I need help with this method, which is to count how many times "hi" occurs in a string.

The code below works with "", " ", "hi" or anything with no more than one "hi" but seems to enters an infinite loop with strings that contain more than one "hi" such as "hihi".

public int countHi(String str) {  int count = 0;    if (str.indexOf("hi") == -1)  // if there is no "hi", return count, which is 0    return count;  else {    for (int i = 0; i < str.length();) {      if (str.substring(i).indexOf("hi") != -1) {          /* if there is a "hi", increment count by 1 and start the loop again        with "i" set as the index of "hi" plus 1, which is that of the letter "i" */                                                  count++;                                  i = str.substring(i).indexOf("hi") + 1;      }      else  // if no "hi" left, exit the loop        break;    }  // for    return count;  }  // 1st else }

I have a small question, in the command shell, what is the difference between typing >java HelloWorldApp and >java -cp . HelloWorldApp to run the HelloWorldApp program, they give the same results (printing out "Hello World") so which of them should I use?

Thank you very much guys for the help.

Liutauras Vilda wrote:@OP

The algorithm you got right, so I guess we just need to clarify, whether you understand why passing pos++ as an argument really was a mistake?

I need to use pos+1 instead because pos++ will only increment pos after the method have used it?

I want to design a method to compute the sum of numbers store in an array using recursion. This is what I have came up with.
    public static double sumOfRealsInAnArray(double[] arr, int pos) { if (pos == arr.length) return 0.0; else return arr[pos] + sumOfRealsInAnArray(arr, pos++); } public static void main(String[] args) { double[] arr = {6.5, 3.2, 6.0, 5.3}; sumOfRealsInAnArray(arr, 0); }
This would cause the said error, I've checked it for anything that could cause the recursion to never terminate but still don't know what's wrong with it. Help :((