Trying to use simple RSA to encrypt text and writing to txt file

My problem is that after inputting a string, I encrypted the ASCII code of the string. The encrypted text will exceed the range of 0~127, and after writing into the txt file that most of them will become '?'. If I read the file, the ASCII code will be 63, so I can't decrypt the string correctly.

Sorry for my bad English, I am confused about this problem.

package test;
import java.io.File;
import java.io.PrintWriter;
import java.util.Scanner;
import java.io.IOException;
public class rsa2 {
    
    public static void main(String[] args) throws IOException{
        
        int p=23;
        int q=11; 
        int N = p*q; //N=253
        int n = (p-1)*(q-1); //n=220
        int e = 7; //public key=(e,N)
        int d; //private key=(d,N)
        int i = 1;
        while((e*i) % n != 1) {
            i++;
        }
        d=i;

        File ifs = new File("HW_Text.txt");
        Scanner input = new Scanner(ifs);
        File ofs = new File("RsaEncryptData2.txt");

        if(!ofs.exists()) {
            System.out.println("file not exists");
        }
        //encryption
        try(PrintWriter output = new PrintWriter(ofs)){
            while(input.hasNext()) {
                String content = input.nextLine();
                for(i=0; i<content.length(); i++) {
                    int M = content.charAt(i);
                    //System.out.print(M+" ");
                    int C = caculate(M,e,N);
                    char c = (char)(C);
                    
                    output.print(c);
                    System.out.print(C+":"+c+" ");
                }
            }
            output.close();
            input.close();
        }
        
        ifs = new File("RsaEncryptData2.txt");
        input = new Scanner(ifs);
        ofs = new File("RsaDecryptData2.txt");

        if(!ofs.exists()) {
            System.out.println("file not exists");
        }
        //decryption
        try(PrintWriter output = new PrintWriter(ofs)){
            while(input.hasNext()) {
                String content = input.nextLine();
                for(i=0; i<content.length(); i++) {
                    int C = content.charAt(i);
                    System.out.print(C+" ");
                    int M = caculate(C,d,N);
                    char ans = (char)(M);
                        
                    output.print(ans);
                    //System.out.print(ans);
                }
            }
            output.close();
            input.close();
        }
}

    static int caculate(int C, int d, int N) {
        int M = 1;
        while(d!=0) {
            while(d%2==0) {
                d=d/2;
                C=(C*C)%N;
            }
            d--;
            M=(M*C)%N;
        }
        return M;
    }
    
}