C++ program to check whether a string is palindrome or not

Write a function that checks whether a string is Palindrome or not. Use this function to check user-entered strings. Also count and display the number of odd or even palindromes in it

#include<iostream>
#include<string>
using namespace std;

static int count_even, count_odd;

void palindrome(string &a)
{
char tmp;
bool chk=false;
int slen=a.length();
string str2=a;

for(int i=0;i<slen;i++)
{
if((a[i]>='a' && a[i]<='z') || (a[i]>='A' && a[i]<='Z'))
chk=true;
else
chk=false;
}

if(chk)
{
// Code to reverse string
for(int n=0;n<slen/2;n++)
{
tmp=a[n];
a[n]=a[slen-1-n];
a[slen-1-n]=tmp;
}
}
else
{
cout<<"\n User entered a non-valid string\n Please enter a new string";
return;
}

if(str2==a)
{
if(slen%2==0)
count_even++; // length of the string is even
else
count_odd++; // length of the string is odd

cout<<"\n Entered string is a palindrome";
}
else
cout<<"\n Enter string is not a palindrome";
}

void count()
{
cout<<"\n\n No. of palindromes (of even length) = "<<count_even<<"\n";
cout<<"\n\n No. of palindromes (of odd length) = "<<count_odd<<"\n";
}

Void main()
{
string str;
char ch;
do
{
system("cls");
cout<<"Enter a string : ";
cin>>str;

palindrome(str);

cout<<"\n\n\n Wanna enter more strings...press (y/Y)\n Press any to Exit\n";
cin>>ch;

}while(ch=='y' || ch=='Y');

count();

system("pause");
}