Boolean

[pennineacute]

I am after some help for a project I am doing pls.

I am writing a program to display the truth table of a boolean expression and so far all is good.

I decided to convert the input into reverse polish notation, so I could get the expression into priority order.  This works.

The program displays the truth table inputs, with no problems, and I am now working on the Boolean part.

If you entered for eg, a+b.c, I have stored the reverse polish notation in a array.  In this would be stored a b c . + in elements 0 to 4

As each row input is calculated eg

a b c    output

0 0 0      

I then want to display the output.

My first idea was to read through the array until I hit a boolean operator and then perform this with the top two variables in my stack, in this case a.b

but when trying values, I can get a boolean output for and, or and xor, but not for NOT, as can be see from the attachment

My program is live at http://andylittlewood.co.uk

The coding I was using to test the boolean output is
 

				echo "1 and 1 = "; echo 1 && 1;
				echo "<br>1 or 1 = "; echo 1 || 1;
				echo "<br> 1 xor 1 = "; echo true ^ true;
				echo "<br>Not 1 = ";echo !(true);

I cannot put my full coding on here, as it is a project and do not want to plagiarise. 

 

[Jacques1]

We cannot help you without seeing the actual code. Don't worry: Nobody will plagiarize a 10-line RPN parser. It's not like this was a novel idea.

 

Generally speaking: You need to know the arity of each operator, because some of them are binary, others are unary (like the negation).

[requinix]

 

echo true ^ true;
echo !(true);

 

You're suffering from PHP's loose typing. ^ is not a logical operator but a bitwise operator. It acts on numbers. true^true is interpreted as 1^1. The answer is, of course, 0.

However ! is a logical operator. !true is false, but PHP decided that the string representation (ie, what you get when you try to echo it) is empty.

 

Try

echo "1 and 1 = "; echo (1 && 1 ? "1" : "0");
echo "<br>1 or 1 = "; echo (1 || 1 ? "1" : "0");
echo "<br> 1 xor 1 = "; echo (1 ^ 1 ? "1" : "0");
echo "<br>Not 1 = "; echo (!1 ? "1" : "0");

or

function showvalue($expr) {
	echo $expr ? "1" : "0";
}

echo "1 and 1 = "; showvalue(1 && 1);
echo "<br>1 or 1 = "; showvalue(1 || 1);
echo "<br> 1 xor 1 = "; showvalue(1 ^ 1);
echo "<br>Not 1 = "; showvalue(!1);

You should also (re)acquaint yourself with PHP's various operators. I suggest you stick with the bitwise operators only, meaning use & and | instead of && and ||.

[pennineacute]

Thanks for that, very much appreciated.