SQL> create or replace procedure test (a number) is
  2  begin
  3    a := 1;
  4  end;
  5  /

Warning: Procedure created with compilation errors.

SQL> show err
Errors for PROCEDURE TEST:

LINE/COL ERROR
-------- -----------------------------------------------------------------
3/3      PL/SQL: Statement ignored
3/3      PLS-00363: expression 'A' cannot be used as an assignment target
SQL> create or replace procedure test (a in out number) is
  2  begin
  3    a := 1;
  4  end;
  5  /

Procedure created.

SQL> 

SQL> create or replace procedure test (a in out varchar2) is
  2  begin
  3    dbms_output.put_line('Before Assignment - Value is :' || a);
  4    a:= 'UPDATED';
  5    dbms_output.put_line('After Assignment - Value is :' || a);
  6    raise_application_error(-20000, 'Test Error');
  7  end;
  8  /

Procedure created.

SQL> 
SQL> declare
  2     test_a varchar2(20) := 'original';
  3  begin
  4     dbms_output.put_line('Before Procedure - Value is :' || test_a);
  5     begin
  6       test(test_a);
  7     exception
  8       when others then null;
  9     end;
 10  
 11     dbms_output.put_line('After Procedure - Value is :' || test_a);
 12  end;
 13  /
Before Procedure - Value is :original
Before Assignment - Value is :original
After Assignment - Value is :UPDATED
After Procedure - Value is :original

PL/SQL procedure successfully completed.

SQL> 
SQL> create or replace procedure test (a in out nocopy varchar2) is
  2  begin
  3    dbms_output.put_line('Before Assignment - Value is :' || a);
  4    a:= 'UPDATED';
  5    dbms_output.put_line('After Assignment - Value is :' || a);
  6    raise_application_error(-20000, 'Test Error');
  7  end;
  8  /

Procedure created.

SQL> 
SQL> declare
  2     test_a varchar2(20) := 'original';
  3  begin
  4     dbms_output.put_line('Before Procedure - Value is :' || test_a);
  5     begin
  6       test(test_a);
  7     exception
  8       when others then null;
  9     end;
 10  
 11     dbms_output.put_line('After Procedure - Value is :' || test_a);
 12  end;
 13  /
Before Procedure - Value is :original
Before Assignment - Value is :original
After Assignment - Value is :UPDATED
After Procedure - Value is :UPDATED

PL/SQL procedure successfully completed.