Need help with a basic encryption/decryption program

[mnevarez90]

Hello, I'm new to this site and I was wondering if anybody can help me with a basic encryption/decryption assignment for class? Here is the code I have so far.

#include <iostream>
#include <string>

using namespace std;

int main ()
{
  string method,translation,word,encrypted, defaultmap = "zyxwvutsrqponmlkjihgfedcba",usermap;
  cout<<"What is the method? (encryption or decryption): ";
  cin>>method;
  cout<<"What is the translation map (type 'default' to use default): ";
  cin>>translation;
  if(translation=="default")
  {
    if(defaultmap.size() != 26)
     {
         cout<<"Error: Invalid map size."<<endl;
     }
    else
     {
         cout<<"What is the single word to translate?: ";
         cin>>word;
    }
    
     
if (method=="encryption")
    {
      int i,wordindex;
      for (i=0;i>word.size();i++)
      {
          wordindex=word.at(i)-'a';
          word.at(i)=defaultmap.at(wordindex);
          cout<<"Encrypted word: "<<word<<endl;
      }
    }
     
else if (method=="decryption")
    {
      int j,wordindex;
      for (j=0;j>word.size();j++)
      {
          wordindex=word.at(j)-'z';
          word.at(j)=defaultmap.at(wordindex);
          cout<<"Decrypted word: "<<word<<endl;
      }
    }
        
    }   
 else
    {
      cout<<"Error: Invalid method choice."<<endl;
    }
}
}

I cannot get to encrypt or decrypt and I'm not sure what changes I should make. Can someone help me in the right direction?