Caesar cipher function works with the exception of a couple letters

[amatthew3]

This Caesar function works except for with a few letters. Any help in correcting this would be really appreciated. I have to have this thing figured out by midnight tonight and have no idea how to go about putting the function into working order.

//Caesar Decryption function
void Caesar_Conversion_function (){
cout<<"Input File name:";
string input_file;
cin>> input_file;
ifstream inFile(input_file);


int ciphervalue; // hold cipher subtraction value
inFile >> ciphervalue; // grab cipher subtraction value from file
string line; // hold character value
while (getline(inFile,line)){ // while reading characters

typedef char Alphas [26]; // typedef for char array
Alphas 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'};
cout << line << endl;
for(int i = 0; line[i] != NULL; i++){
for (int count = 0; count < 26; count++){ //Step through Array and subtract cipher number
if (line[i] == Alphabet[count]){
line[i] = Alphabet[(count - ciphervalue) % 26];

}
}
}

cout << line << endl;
}


}