Thread: Palindromes

jewelz, you're still plagued by a basic misconception about how functions work.

a function only returns at most ONE value each time it is called. a function with a return type specification of void never returns a value.

a return statement immediately stops execution of the function and returns the variable specified by the argument of the return statement.

so, in your pseudofunction above, the for loop accomplishes nothing, because the function will return rit on the first iteration, which is exactly equivalent to:

Code:

return s.rbegin();

the basic anatomy of a function is as follows:

Code:

// a free function (i.e. a function that is not a member function of a class)
returnType functionName(/*argument list here*/)
{
// function body
return instance_of_returnType;   
}

// a class-member function
returnType className::functionName(/*argument list here*/)
{
// function body 
return instance_of_returnType;
}

you would use a function like this:

Code:

#include <vector>
std::vector<int> countTo(unsigned int number)
{
     std::vector<int>countList;
     for(unsigned int i=0;i<number;i++)
     {
          countList.push_back(i+1);
     }    
      return countList;
}

int main(int argc, char* argv[])
{
      std::vector<int> oneToTen = countTo(10);
}

note how the vector is populated over the course of the function execution and then ONE result is returned.

If you are allowed to use std::string::reverse_iterator, then from original_string.rbegin() to before original_string.rend(), copy to the new string.

If you must use indices, then copy the original string into a new string, then reverse the old string by swapping the nth character with the nth last character, all the way from the character at position 0 to the middle of the string.

ok guys, so now i have to write a main function that will read words from input and print out all the palindromes, each being on a seperate line..

so first of all my professor said to use the bool palindrome function in terms of the reverse, so i came up with this:

Code:

bool Is_Palindrome(const std::string& s)
{

if (s==reverse(s))
return(true);
else
return(false);

}

and as for the main function should i do something like:

Code:

int main()
{
string s;
cout << "Input some words ";
getline (cin, s);
if (if (Is_Palindrome(s)==true)
cout<< s <<endl;

return 0;

}

i tried compiling it, but it gave me some really weird error..and its not even pointing at specific lines..

anyway let me give u guys the format i have for this program maybe it will help:

i have a header file called pal.h :

Code:

#ifndef GUARD_pal_h
#define GUARD_pal_h

#include <iostream>

std::string reverse(const std::string& s);
bool is_palindrome(const std::string& s);

#endif

a file called pal.cc which includes the definitions of the above functions:

Code:

#include "pal.h"
#include <string>

using std::string;

//function declaration
std::string reverse(const std::string& s)
{
    string s2 = "";
    for (int i = 1; i < s.length(); i++)
	{
	    s2 = s2 + s[s.length() - i];
	}
    s2 = s2 + s[0];
    return s2;
}

bool Is_Palindrome(const std::string& s)
{

    if (s==reverse(s))
	return(true);
    else
	return(false);

}

and as for the main function i posted above i included "pal.h" and "pal.cc" and then the appropriate declarations and usings..what might be the problem?

Originally Posted by EVOEx

Well, your earlier method, the IsPalindrome function on the first page, is a lot better... Why even both reversing it all? I don't understand why your professor should say something like that... As a bad hint or as yet another silly must?

yeah i understand what you're saying, but the project description says we need both functions -_-