GCD

Xml :

<?xml version="1.0" encoding="utf-8"?>

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<EditText
    android:id="@+id/etnum1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:ems="10"
    android:inputType="number"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.412"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.091" />

<EditText
    android:id="@+id/etnum2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:ems="10"
    android:inputType="number"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.412"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/etnum1"
    app:layout_constraintVertical_bias="0.082" />

<Button
    android:id="@+id/btn"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="GCD"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.435"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/etnum2"
    app:layout_constraintVertical_bias="0.157" />

<TextView
    android:id="@+id/tv"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="TextView"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.439"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/btn"
    app:layout_constraintVertical_bias="0.198" />

</androidx.constraintlayout.widget.ConstraintLayout>

Java :
package com.example.gcdtwonumbers;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

private EditText num1;
private EditText num2;
private Button button;
private TextView tv;


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

    num1 = (EditText)findViewById(R.id.etnum1);
    num2= (EditText)findViewById(R.id.etnum2);
    button = (Button)findViewById(R.id.btn);
    tv = (TextView)findViewById(R.id.tv);

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            int gcd=1;
            int number1 = Integer.parseInt(num1.getText().toString());
            int number2 = Integer.parseInt(num2.getText().toString());
            for(int i = 1; i <= number1 && i <= number2; i++)
            {

                if(number1%i==0 && number2%i==0)


                    gcd = i;
            }
            tv.setText(String.valueOf(gcd));

        }
    });
}

}