string array omiting characters z and y - c++

Question

im doing an assignment for my lab which has to do with encrypting a string into a text file from another file, and it works good but my only problem is that when i encrypt or decrypt the encryption omits the letter Z and Y. I've tried changing a couple of things but nothing works, please if you know how to explain because i am lost.
this is my code so far:
#include iostream
==
#include fstream
==
#include cstring
==
#include string
==
using namespace std;
int main()
{
ifstream inputFile;
ofstream outputFile;
const int SIZE=150;
char file[SIZE];
char message[SIZE+1];
char letter;
char alphabet[]={'A','B','C','D','E','F','G','H','I','J','K','L',
'M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z','\0'};
cout<<"Enter the message you want to encrypt: "<<endl; //getmessage
cin.getline(message,SIZE,'\n');
for(int i=0;i<strlen(message);i++){
if(islower(message[i])) //change to
message[i]=toupper(message[i]); //uppercase
}
outputFile.open("textoNoEncrypt.txt");
for(int i=0;i<strlen(message);i++){ //copy message to
outputFile.put(message[i]); //file
}
outputFile.close();
inputFile.open("textoNoEncrypt.txt");
if (inputFile.is_open()){
int i=0;
while (!(inputFile=='\0')){
inputFile>>file[i]; //reading and copying
i++; //data from file
}
}
inputFile.close();
outputFile.open("textoEncrypt.txt");
for(int i=0;i<strlen(file);i++){
int j=0;
int P=0;
int index=0;
bool found=false;
while(!found){
if(file[i]==alphabet[j]){
P=j;
index=(P+3)%26; //encrypting message
file[i]=alphabet[index];
found=true;
cout<<j<<" ";
}
j++;
}
outputFile.put(file[i]);
}
outputFile.close();
cout<<message<<endl; //show original message
cout<<file<<endl; //show encrypted message
return 0;
}

Answer 1

I think this is cause by the P+3 line