How to pass integer from one Activity to another?

It’s simple. On the sender side, use Intent.putExtra:

Intent myIntent = new Intent(A.this, B.class);
myIntent.putExtra("intVariableName", intValue);
startActivity(myIntent);

On the receiver side, use Intent.getIntExtra:

 Intent mIntent = getIntent();
 int intValue = mIntent.getIntExtra("intVariableName", 0);