11 replies to this topic

[ahmed]

Help with this one.
1.Write a program which will tell that entered string is palindrome or not. Make a function which takes a character array and also an integer array entered by user prints whether string is palindrome or not.


The problem is how to make the function of it?I just know how to take the string and have no clue how to reverse it and check it?any tips?

[WingedPanther]

Step 1: look up the string functions that are available. Also, the answer will depend a LOT on whether this is C or C++.

[ahmed]

offcourse i am using C++ , but i dont know how to make its function :(

[WingedPanther]

I would us rbegin and rend to create iterators to march through the string in opposite directions.

You can use 2 indices to do the same thing with the integer array.

[lucuis]

The simpest way is to run a loop in both direction. One starting from 0 and second starting from length - 1. Compare symbols at each step and if they differs return false. Have you already made some code?

[JGRobinson]

I would just copy and reverse the string, and see it they are both equal.

[dcs]

My recommended approach:

• Have the function receive a const string.
  
  
• Allocate space for a copy of the incoming string.
  
  
• Copy the incoming string element by element as lowercase if it is alphanumeric. That is, skip whitespace and punctuation.
  
  Consider the following as a test case.
  

  const char one[] = "A Man, A Plan, A Canal-Panama!";

  The lowercase alphanumeric-only copy would be:
  

  amanaplanacanalpanama

  
  
• Then compare beginning and ending iterators, as mention by WingedPanther, incrementing the beginning and decrementing the ending until the beginning is past the ending. If the elements don't match, it's not a palindrome; if you make it all the way through, it is a palindrome.

[lucuis]

Re: dcf

You approach is simple, but contains a lot of needless work. For instance, you can iterate in both directions and skip punctuation "on the fly". Also, what for should you copy a string, if it isn't changed inside the function!?

[Aereshaa]

It is changed. You are removing punctuation and capitalization, so don't change the original string, allocate a copy!

[dcs]

lucuis said:

You approach is simple, but contains a lot of needless work. For instance, you can iterate in both directions and skip punctuation "on the fly".

True enough, but more complex. As this is usually a beginner's exercise, my recommendation was not an exercise in efficiency -- rather one in which the basics are more approachable. After the copy, the single-case no punctuation version can be printed for easier debugging, for example. Making a copy is a safeguard in case the function is passed a string literal.

Frankly, if the OP would post an attempt, it would be easier to continue critiques in the direction you mention.

[ahmed]

this is my ultra failed attempt to just reverse the the char array hope u can help with it and il do with the rest of comparing

{
   clrscr();
   int i;
   char array[10],t;
   cout<<"\n Enter Name : ";
   gets(array);
   for(i=array[i];array[i]=<0;i++)
   t=array[i-1];
        cout<<array[i];
   getch();
   }

[chili5]

JGRobinson said:

I would just copy and reverse the string, and see it they are both equal.

Don't do this. A more effective way is to loop through the character array and check the char at the beginning with the char at the end, and if at any point you find two chars that don't match return "false" and against the method.

Using the reverse method you are being wasteful as you are checking the entire string. If the first char at the beginning and the char at the end don't match then why check the rest of the string? You know it's not a palindrome.

bool isPalindrome(string sLine) {

	int nFirst = 0;

	int nHigh = sLine.length()-1;


	while (nFirst < nHigh) {

		if (sLine.at(nFirst) != sLine.at(nHigh)) {

			return false;

		}

		nFirst++;

		nHigh--;

	}

	return true;

}