How to how to return a integer value from cpp file to Java class

[zachary lim]

hi all, I am new here as well as new to Android C++ JNI

Essentially my problem is this: I want to display start-up.cpp into the Toast, everything else works until i added useful_cpp then it crashes, may i know what went wrong?
every step i take, i go backwards 2 times, every time i think i got the concept, the next time i demonstrate it, it crashes again, it is actually like redoing C++ from scratch all over again lol, thanks for your help and please be patient with me, thank you!

These are my details:
start-up.h---------

using std::endl;
using std::printf;
using std::string;
using std::stringstream;

#ifndef NDKTEST_USEFUL_CPP_H
#define NDKTEST_USEFUL_CPP_H

class useful_cpp {
    public:
    useful_cpp()
    {

    }
    int Result()
    {
        int output1 = 1;
        int output2 = 2;

        int result = output1 + output2;
        //output = result;
        //const char *res = output.c_str();
        return result;
    }
};
#endif //NDKTEST_USEFUL_CPP_H

start-up.cpp--------

#include <jni.h>
#include <string>
#include "useful_cpp.h"
using std::string;
using std::stringstream;
extern "C"

JNIEXPORT jint JNICALL Java_beginnerapps_MainActivity_integer(JNIEnv *env, jobject /* this */)
{
    useful_cpp usefulCpp;
    int returnCpp = usefulCpp.Result();
    
    return returnCpp;
}

MainActivity.java---------------

public class MainActivity extends AppCompatActivity {

    // Used to load the 'native-lib' library on application startup.
    static {
        //load the library - name matches jni/Android.mk
        System.loadLibrary("native-lib");
        System.loadLibrary("ndkfoo");
        System.loadLibrary("HelloWorld");
        System.LoadLibrary("useful_cpp");
    }

    public native String helloWorld();
    public native String string();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Example of a call to a native method
        TextView tv = (TextView) findViewById(R.id.sample_text);

        //this is where we call the native code
        String hello1 = stringFromJNI();
        String hello2 = string();
        String hello3 = helloWorld();
        int hello4 = integer;
        String intHello = Integer.toString(hello4);

        tv.setText(hello1 + "\n" + hello2 + "\n" + hello3   + "\n" + intHello + "\n");
        Toast.makeText(this, hello1 + "\n" + hello2 + "'\n" + hello3 + "\n", Toast.LENGTH_LONG).show();
        //create AlertDialog
        new AlertDialog.Builder(this).setMessage(hello1 + "\n" + hello2 + "'\n" + hello3 + "\n").show();
    }
     public native String stringFromJNI();
     public native int integer();
}

[mic _]

> int hello4 = integer;

How does that even compile? You left out the parentheses for the method call.

If you are indeed getting a runtime error, you should start by inspecting the stacktrace from logcat.

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[zachary lim]

Oh drats, i forgot to create the function caller /flipstable

Thank you very much!