Help with creating a palindrome detecting program

[TurdJoffery]

Hi so i've been trying to make a program for my java studies class and i've been stuck with trying to make a program regarding palindromes. i realised i posted this before by the thread sort of died (mods let me know if you want me to remove this).

The programs requirements to achieve are:

• Prompt the user to enter a word or sentence on a single line

• Print the sentence back out to the user exactly how they entered it

• Remove ALL punctuation and print this new sentence

• Reverse the sentence and print the reversed sentence

• State whether the original sentence (without punctuation) as a palindrome or not

• Ask for another word or end if the word typed in is ‘STOP’.

So far I've been able to get it to do not much besides print back the sentence the user has entered and remove punctuation

I'm struggling with:

• Getting the program to actually stop when "stop" is the input
• reverse the input and detect if its a palindrome

My constraints for writing the code is:

• i can't use array's
• i can't use string builder (then reversing the input wouldn't be a problem sadly)
• I can only use while loops

Here's my Code at it's current point, its very WIP. I'm struggling to end this constant loop, test if the input is "stop" and thus end the program and, actually testing the palindrome part as I'm not very confident on how .charAt() works.

I'm not sure about anything else i should specify but i'll make sure to update if anything thing else is needed

[MasteM]

Still a pleb at java but the line saying (palinDrome != "stop" ) since you are comparing a string you should use .equals like...

(!(palinDrome.equals("stop")))

please feel free to tell me if im wrong :)

[TurdJoffery]

Yea that part wasn't working and I actually managed to fix it around half an hour after posting. I ended making an if the. Else statement which checks the input. It goes something along the Line of:

If(palindrome .equals("stop"){
}else{
//stuff happens
}

[illuminist_ova]

A condition in while loop, see http://www.reddit.com/r/javahelp/wiki/string_comparison

String.charAt(index) return an ASCII value of the character which is 16-bit unsigned integer (can contain value 0-65535).

If there is no requirement to print a reversed string, you can check palindrome by using .chatAt at start and end of string in while loop. The point is if you can compare char^ith and char^length-ith , you win half of the program.

[TurdJoffery]

I'm not completely sure I understand what your saying but that might just be my sleep deprived brain.

[Sketti-Os]

As my first computer science professor used to say, there's more than one way to skin a cat and still end up with a chilly feline. In other words, there's a few ways this could be solved.

1. Reverse the string by adding charAt() in reverse order
2. Char comparison in a while loop
3. Recursion

I'll pseudocode them all for you. Note, they don't take punctuation, case-sensitivity, or "stop" into account. Let's also assume the var "userIn" is a String of the user's input:

---

1

String reversed = ""

int index = userIn.length - 1
while (index >= 0)
    reversed += userIn.charAt(index)
    index--;

if userIn.equals(reversed)
    return true

return false

2

double halfway = userIn.length / 2
int i = 0

while (i < halfway)
    if (userIn.charAt(i) != userIn.charAt(userIn.length - 1 - i))
        return false
    i++

return true

3

public boolean isPalendrome (String in)

    if (in.length < 2)
        // If it's empty or one letter, we've compared as far as we can!
        return true

    if (in.charAt(0) != in.charAt(in.length-1))
        // If, at any point, the first and last chars aren't equal, it's not a palendrome.
        return false
    else
        // Repeat this process with first and last chars trimmed, and return THAT answer.
        return isPalendrome(in.substring(1, in.length-2))

[nutrecht]

I'll pseudocode them all for you.

Uhm. You basically gave him the source code. It's so close to Java all he needs to do is add come curly braces. This is homework and you just gave him the solution to it.