Simple logic is kicking my butt.

[Robert Brown]

im having a problem here and it seems I just cannot get my logic right.

this is in a class

 	boolean move( char ch, int row, int col){
		
		if (ch != 'X' || ch != 'x' || ch != 'O' || ch != 'o'){
			System.err.println("Invalid input. Must be 'X' or 'O'. You entered " + ch);
			return(false);
		}
		if (board[col][row] != '\0'){
			System.err.println("That space is taken");
			return(false);
		}
		else{
			return(true);
		}
	}   

and this is what is in my driver

  		TicTacToe board_0 = new TicTacToe();
		
		board_0.move('X', 1, 1);
		board_0.move('x', 1, 1);
		board_0.move('O', 1, 1);
		board_0.move('o', 1, 1);
		board_0.move('a', 1, 1);
		board_0.move('d', 1, 1);  

no matter what it will not get past the first if statement and returns my "invalid input" error. What did I do wrong thanks for any help

[Paul Yule]

um. Don't hit yourself too hard but lets pretend that you input 'O' ... the first OR in your if statement will evaluate to true and kick you down. I think you mean to have used
( ch != 'X' && ch != 'x' && ch != 'O' && ch != 'o')... if it isn't ANY of those...go in there. Not if it isn't just one of those cases.

[Robert Brown]

Thank you very much. I knew it was something too simple, can't believe I missed that; Moral of the story.... caffeine != a substitute for sleep.

[Campbell Ritchie]

Welcome to JavaRanch

Putting !() round your test would sort it out. You can use different formulae; look up de Morgan's Law for how to convert between || and && when there are nots around.