VS 2012 Calling Modules

i am have written 4 modules and called them all at once when saving my application.

Call Transaction_New_Validate()
Call Decision_Validate()
Call Client_Exist_Save()
Call Client_Search()
Call Transaction_Save()

the problem is that when an error occurs in the first module, it carries on to call the next one.

how do i make it stop when an error occurs on the first one without writing all of them in one module.

thanks