palindromic numbers function

[DJPuffNStuff]

Hello every one. I am new to programming so i am sorry if this is a simple question. I am trying to write a function that will return "True" if the number I hand it is palindromic.

Here is my code.

#include <iostream>
#include <string>
#include <cstdlib>

using namespace std;

bool palin_test(string str);

int main()
{

string test = "999";

cout << sizeof(test) << " size of String" << endl;
cout << test << endl;

cout << palin_test(test);



}

bool palin_test(string str) {

bool mark = 1;     // Set value to return
string newstr;        // New string variable

if ((sizeof(str) - 1) <= 1) {    // make sure value is greater than one
    return mark;      // if one, return true
}

if (atoi(str[0]) == atoi(str[(sizeof(str) - 1)])) {    //test first digit and last digit to see if equal.

cout << "\ntest";

newstr = str;     // remove first and last digit.
newstr.erase(0, 1);
newstr.erase((sizeof(newstr) - 1), 1);
palin_test(newstr);            // recursive call of new string
}
cout << str << " New string" << endl;
cout << sizeof(str) << " size of String" << endl;
return (mark = 0);
}

When I try to compile this I keep getting errors at line 32. This code is still a work in progress so I need to polish it up a lot but it seems to me it should work, although obviously it doesn't. :)
P.S sorry about all of the random "cout" statements. I was using them to de-bug.

Thanks for the help.

[cire]

atoi takes a c-string argument. It does not take a single char. A conversion seems like overkill here, anyway. Just directly compare the first character to the last character. Note that sizeof(std::string) does not give you the length of the string.

if ( str[0] == str[str.size()-1] ) {
// ... 

[DJPuffNStuff]

Thanks for the response Cire. I tried what you suggested and it worked great. But I am not getting the function to return the result I want. I have been working on it for a few hours and cannot locate the issue. Here is my new code.

#include <iostream>
#include <string>
#include <cstdlib>

using namespace std;

bool palin_test(string str);

int main()
{

string test = "99999";


cout << palin_test(test);



}

bool palin_test(string str) {

bool mark = 0;           // Set value to return
string newstr;        // New string variable
char a = str[0];
char b = str[str.size() - 1];

if (str.size() <= 2 ) {    // make sure value is greater than one. "2" is due to null operator.
mark = 1;
cout << " mark is " << mark << endl;
return mark;         // if one, return true
}

cout << " String before first if " << str << endl;

cout << " A is " << a << endl << " B is " << b << endl;

if ( a == b ) {    //test first digit and last digit to see if equal.

newstr = str;     // remove first and last digit.
newstr.erase(0, 1);
newstr.erase(newstr.size() - 1, 1);
cout << " New String size is " << newstr << endl;
palin_test(newstr);            // recursive call of new string
}

return mark;              // return "0"

}

The number passed to this function should return a value of 1 or true but I keep getting a 0 or false. I think the problem might be in the if statement at line 28 but I can't find it. If any one can point out what I am missing I would very much appreciate it. Thank you

[DJPuffNStuff]

Never mind. I just figured out where my mistake was.
palin_test(newstr); This needs to be: mark = palin_test(newstr);
Thanks all.

[TheIdeasMan]

When I did this years ago, I just reversed the string then compared it to the original.

When using booleans, just use true or false (not 0's or 1's)- you won't need the mark variable at all. Technically it doesn't matter whether you use 0 or 1, but the bool variable was invented because true or false are easier - so I prefer to not mix the 2 concepts.

HTH

[TheIdeasMan]

Instead of palin_test returning a bool - would it not make more sense to return the remaining part of the string?