Reverse an array without affecting special characters

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

int isalpha(char c)
{
return ((c>='a'&&c<='z')||c>='A'&&c<='Z');
}
int main()
{
string s="a,bc";
int n=s.length()-1;
int i=0;

while(i<n)
{
if(isalpha(s.at(i))&& isalpha( s.at(n)))
{
char t=s.at(i);
s.at(i)=s.at(n);
s.at(n)=t;i++;n--;
}
else if(!isalpha(s.at(i))&&isalpha(s.at(n)))
i++;
else if(!isalpha(s.at(n))&&isalpha(s.at(i)))
n--;
else
i++,n--;
}
cout<<s;
}