Smartform-Suppress Zero and Display Zero for same field in Diff Conditions?

Hi,

I have a scenario in smartform, where for a quantity field of length p15 and Dec3, needs to display ZERO for one scenario and display SPACE for another condition. To display ZERO i have made it as &quantity(c)&, so that i can display zero. It displays ZERO, but for another condition, when i want to display space, there also it displays 0.000 ! how to display SPACE there ?

thanks,

Padma