PRAGMA EXCEPTION_INIT – allows one to map ORA- error and it can be raised in PL/SQL code. The SQL Error number passed in “EXCEPTION_INIT” is the same as error code except for “NO_DATA_FOUND” ORA-01403 which is 100.
See http://docs.oracle.com/cd/B19306_01/appdev.102/b14261/errors.htm#BABGIIBI – Summary of Predefined PL/SQL Exceptions

Example:
declare
no_rows_found exception;
pragma exception_init(no_rows_found, 100);
begin
raise no_rows_found;
end;
/
*
ERROR at line 1:
ORA-01403: no data found
ORA-06512: at line 4

declare
too_many_rows exception;
pragma exception_init(too_many_rows, -1422);
begin
raise too_many_rows;
end;
/
*
ERROR at line 1:
ORA-01422: exact fetch returns more than requested number of rows
ORA-06512: at line 5