Given a string, shift the characters to given kth position

Given a string, shift the alphabets of the string to plus "K"th position.
For Example: If the given string is "abcdefg" and the shift K= 3
                     Then the output is "defghij"

Implementation:
#include <iostream>
using namespace std;

int main() {
  int N,K;
  cin>>N;
  char ch[N];
  cin>>ch;
  cin>>K;
  for(int i=0;i<N;i++)
  {
    if((ch[i]>='a' && ch[i]<='z') || (ch[i]>='A' && ch[i]<='Z'))
    {
      if(ch[i]+K<='z')
       cout<<char(ch[i]+K);
     else
      cout<<char(ch[i]-26+K);
   }
  
   else
   cout<<ch[i];
  }
  return 0;
}