package com.chapter.BJ.UpperLower;

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        String str = sc.nextLine();

        for (int i = 0; i < str.length(); i  ) {
            if (str.charAt(i) >= 65 && str.charAt(i) <= 90) {
                str.charAt(i)  = 32;
            } else if (str.charAt(i) <= 122 && str.charAt(i) >= 97) {
                str.charAt(i) -= 32;
            }
            System.out.print(str.charAt(i));
        }
    }

}

Hello everyone, I don't understand why I get an error on str.charAt(i) = 32; and str.charAt(i) -= 32;. Thank you for your help.

CodePudding user response：

str.charAt(i) merely returns the character at that index. I assume you want to alter the character at that index, so what you are looking for is something like this.

CodePudding user response：

The charAt() method simply returns the character at the specified index in a string. Its source code is below. It is an R-value and can be only used on the right side of assignment statements. But str.charAt(i) = 32; is equivalent to str.charAt(i) = str.charAt(i) 32;, so you may get expected variable error.

public char charAt(int index) {
   if ((index < 0) || (index >= value.length)) {
        throw new StringIndexOutOfBoundsException(index);
   }
   return value[index];
}

You can introduce a local variable to store stc.charAt(i) and update it as you need, like this.

for (int i = 0; i < str.length(); i  ) {
    char c = str.charAt(i);
    if (str.charAt(i) >= 65 && str.charAt(i) <= 90) {
        c  = 32;
    } else if (str.charAt(i) <= 122 && str.charAt(i) >= 97) {
        c -= 32;
    }
    System.out.print(c);
}

If you need to update str simultaneously, consider StringBuffer or StringBuilder since String is an immutable object.