Convert a string to number

Hi.

I want to set a value such as 1.5 or 10 to a text box in a report
datawindow at the run time. The value will come from the user before
**** runs the report. How do I convert this string in the text box to
a number that will be used for further computation at the summary band?
I tried number() function, but it requires a real string and refuses to
accept a variable or a column name. Thanks in advance for any help.

Jian Kuang

If the value comes from the user, it would be in the form of a Retrieve
Argument. You can refer to the retrieve argument in the computed field for
further calculation. If the retrieve argument is al_num, your computed field
in summary band will look like : column_name + al_num. // any computation

Thanks