oracle sql not accepting the input from the user - sql

Question

Whenever i try to run a program consisting of user input the compiler always throws the same error of i dont know what that means. the error does not explain what the error is that i am encountering, can anyone please help regarding this problem.
Here is the error:
Unsupported Command
Unsupported Command
ORA-06550: line 6, column 4:
PLS-00103: Encountered the symbol "&" when expecting one of the following:
( - + case mod new not null <an identifier>
<a double-quoted delimited-identifier> <a bind variable>
continue avg count current exists max min prior sql stddev
sum variance execute forall merge time timestamp interval
date <a string literal with character set specification>
<a number> <a single-quoted SQL string> pipe
<an alternatively-quoted string literal with character set specifi
Here is the code for plsql in which i am taking user input for temperature and returning the celcius or farenheight temp of the same.
declare
f number;
n number;
ch char;
begin
f:=&f;
ch:=&ch;
if(ch!='F') then
n:=(f-32)*5/9;
else
n:=(f*9/5)+32;
end if;
dbms_output.put_line('Temperature: '||f||' '||ch);
end;
/
I would be highly grateful for your efforts.
Thank you

Answer 1

The & syntax indicates the variable is a substitution variable which is processed in the client application (it is effectively a find-replace on the variable).
Substitution variables are only supported by a limited number of client applications (including SQL*Plus and SQL Developer); they are not supported in other applications such as Oracle Apex, Java, C#, Python, etc.
You are getting the error because your client application does not support substitution variables; instead, you need to use the correct syntax for the application you are using (which may be to use bind variables).

Answer 2

This can be run in the "SQL Commands" window in apex, but you need to use the bind variable syntax :
declare
f number;
n number;
ch char;
begin
f:=:f;
ch:=:ch;
if(ch!='F') then
n:=(f-32)*5/9;
else
n:=(f*9/5)+32;
end if;
dbms_output.put_line('Temperature: '||f||' '||ch);
end;
/
This will invoke a popup window in which you are prompted for the values of :F and :CH.