为什么 A 不是变量？

Question

aa[i1] takes the user input and breaks it into single chars. For example: dog becomes d, o, g. I have an if statement which if aa[i1] is equal to "A", "B", "C"... it'll tell the user so. The error is when aa[i1] == A, A isn't a variable?

Answer 1

First, please never post code as an image. Second, I've replaced your prompt and input with a constant for the sake of demonstration. Third, you need to surround your constant characters with single quotes (to make them constant characters, or you could define a character constant final char A = 'A'; ). Fourth, String has a method for copying its' internals to a char[] . Finally, I would prefer printf to string concatenation. Like,

String a = "ANGRY AARDVARK";
char[] aa = a.toCharArray();
for (int i = 0; i < aa.length; i++) {
    System.out.printf("Character at index %d=%c%n", i, aa[i]);
    if (aa[i] == 'A') {
        System.out.println("Character is A");
    }
}