试图更好地掌握循环逻辑。

Question

I hope your Sunday is going well. So my goal in this little program is to print a new string with indexes [0,1] [4,5]...[12,13]... The loop functions only with an even numbered word that's greater than 4 letters. Why is this? Any advice on how to polish this turd would be greatly appreciated. Thank you.

import java.util.Scanner;

public class LoopPractice {
public static void main(String[] args) {

  Scanner myScanner = new Scanner(System.in);

  System.out.print("Enter a String please: ");
  String str = myScanner.next();

  int count = 0;
  int x = 0;
  int y = 1;
  String emptyStr = "";

     while ( count != str.length() ) {

        emptyStr += str.charAt(x) + "" +  str.charAt(y);
        x += 4;
        y += 4;
        count += emptyStr.length();
     }
  System.out.print(emptyStr);

}
}

Answer 1

I am not 100% sure of your question, but the problem seems to be lying here: x += 4; y += 4; x += 4; y += 4; . You are incrementing those two variables by 4 each time (0, 4, 8 for X and 1, 5, 9 for Y).

When you are using the .charAt function, you are most likely getting an error which denotes some out of bounds issue since the values for X and Y are larger than the length of the string.

You will need to change the way that X and Y are incremented for you to stop getting that error.

Answer 2

While condition, should check if you are not overflow string index:

import java.util.Scanner;

public class LoopPractice {
public static void main(String[] args) {

  Scanner myScanner = new Scanner(System.in);

  System.out.print("Enter a String please: ");
  String str = myScanner.next();

  int x = 0;
  int y = 1;
  String emptyStr = "";

     while ( y <= str.length() ) {

        emptyStr += str.charAt(x) + "" +  str.charAt(y);
        x += 4;
        y += 4;
     }
  System.out.print(emptyStr);

}
}

Answer 3

This is all what you need :

System.out.print("Enter a String please: ");
String str = myScanner.next();
while(!str.isEmpty()){
          System.out.println(str.charAt(0)+""+str.charAt(1));
          if(str.length()>4)
              str = str.substring(4);
          else
              str = "";
     }

Answer 4

The problem is this line

count += emptyStr.length();

Your emptyStr gets longer by two characters every time. So the first time through, you add 2 to count . The next time, you add 4, then 6, and so on. So count takes the values 0, 2, 6, 12, 20 and so on.

If str.length() isn't one of those values, your loop will never end.