Crystal Reports formula problem

Message

Hi.
Below is the contents of a formula.

Local StringVar strGST;
strGST := "";
if {proc_RptCruise_TMFT;1.GST_Z} > 0 then
        strGST:= {@tZSum};
if {proc_RptCruise_TMFT;1.GST_O} > 0 then
        strGST:= strGST + {@tOSum};
if {proc_RptCruise_TMFT;1.GST_J} > 0 then
        strGST:=strGST + {@tJSum};
if {proc_RptCruise_TMFT;1.GST_V} > 0 then
        strGST:=strGST + {@tVSum};

Now the problem is if any of the if condition proves to be false then the formula is showing empty.

For ex : if 1, if 2 fails , if 3 return true and if 4 fails then the content assigned from if 3 also vanishes from strGST.

How to overcome this problem  

Thanks 

Seenivasan