C++ palindrome not working - c++

Question

I wanted to create function that returns true/false according if the input is a palindrome or not, when given abcddcba or aba it does not give true, but it should . plz help
bool checkPalindrome(char input[],int p=0) {
if(input[1]=='\0'){
return true;
}
if(sizeof(input)%2==0) {
int a = sizeof(input);
for(int i=0;i<(a/2);i++) {
if(input[0+i]==input[a-i-2]){
p++;
}
}
if(p==a/2){
return true;
} else{
return false;
}
}
else{
int a = sizeof(input);
for(int i=0;i<((a-1)/2);i++)
{
if(input[0+i]==input[a-i-2]){
p++;
}
}
if(p==(a-1)/2){
return true;
} else{
return false;
}
}
}

Answer 1

C++ style:
bool checkPalindrome(const std::string& str)
{
size_t len = str.size();
for (size_t i = 0; i < len/2; i++)
{
if (str[i] != str[len-1-i])
return false;
}
return true;
}
C style:
bool checkPalindrome(const char* str)
{
size_t len = str ? strlen(str) : 0;
for (size_t i = 0; i < len/2; i++)
{
if (str[i] != str[len-1-i])
return false;
}
return true;
}
In either case, you may need to evaluate (ask) if an empty string should be considered a palindrome or not.

Answer 2

your code is too long. There's a simple way: iterating once over the elements of the string comparing the n-1 with 0 and n-2 with 1 and so on.
If two characters are not identical return false otherwise continue checking:
bool checkPalindrome(char* str) {
const int size = strlen(str);
for(int i(0), j(size) - 1); i < size / 2; i++, j--)
if(str[i] != str[j])
return false;
return true;
}
int main(){
char* str = "level";
cout << checkPalindrome(str);
cout << endl << endl;
return 0;
}

Answer 3

C++ version based on strings and iterators (only for the sake of completeness, the other answers are already very nice) :
bool checkPalindrome(const string& str) {
for (auto p = str.begin(),q = str.end(); p!=q && p!=q+1; p++ )
if (*p!=*--q) // if char from front doesn't match char from rear ?
return false; // then it's not a palindrome !
return true;
}
Explanations: the iterator p starts at the front of the string and q at the rear (after the last char). p will advance and q will go backwards. If p reaches q or if p has passed q (special case if the word has an even length), it's over and we can conclude a palindrome. But if before, there is any difference between the char at p and the char preceeding q , it's not a palindrome.
Online demo, with little test suite