Please suggest correction in this pl and sql code

Question

Hi,
Please find the error in following PL/Sql code and suggest the corrections.
I want to use this code on form-trigger level to display error messages in middle of the screen.
When I compile this code in ONERROR trigger, it is showing compiling errors.
Code:
ERR_VAL NUMBER(5):= NVL(ERR_IN,ERROR_CODE);
MSG VARCHAR2(150) := NVL(MSG_IN,SUBSTR(' '||ERROR_TYPE||'-'
||TO_CHAR(ERR_VAL)||': '||ERROR_TEXT,1,150));
Compilation time errors:
Error 103 at line 1,column9
Encountered the symbol “NUMBER” when expecting one of the following:
:= [ @ %
the symbol “=” was substituted for “NUMBER” to continue
Error 103 at line 1, column 27
Encountered the symbol”=” when expecting one of the following:
.[=%=.+</> in mod not rem an exponent(**)
<> or !=~=>=<=<> and or like between is null is not ||
is dangling
the symbol “ was inserted before”=” to continue.
Error 103 at line2, column5
Encountered the symbol “VARCHAR3” to continue.
Error 103 at line2,column 20
Encountered the symbol”=” when expecting one of the following:
.[=%=.+</> in mod not rem an exponent(**)
<> or !=~=>=<=<> and or like between is null is not ||
is dangling
the symbol “ was inserted before”=” to continue.
thanks in advance
prasanth

Answer 1

Is this the whole content of your trigger? In PL/SQL you have to declare variables under the declare section and then to make the program under begin:
declare
VAR1 xxxxxx;
VAR2 xxxxxx;
begin
/* assignments */
end;
I am not sure if it is possible to make your assignments with error_code etc. in the declaration. Where you are calling the message-box?
Can you give us the complete content of your form-trigger?