Try initializing the c with some value, because right now you are creating an empty array with no storage allocated.
> a = 100.0
> b = 10.0
> c = [0.0] # or Array(Float64,1)
> ppmm = ccall((:multiply_, "/home/juser/ManUTD/fortran_try/fsbrtn"),
> Void,(Ptr{Float64},Ptr{Float64},Ptr{Float64}),&a,&b,c)
> println(c)
>
>
