Write data to output file

Question

since I am new to Wolfram Mathematica I am wondering if somebody can help me with my problem. (it is simple I guess)

Basically I would like to extract the data from a function I defined in Mathematica an write this data to a output file (for instance a .dat file)

Here's my function:

w[x_]=0.00142878 Sin[3.14159 x]

Now I would like to fill the first column of the output-file with the data of w. Therefore I did the following loop and to show you the results I displayed the output.

For[x = 0.0, x <= 1, x += 0.2, PutAppend[w[x], "w.dat"]]

FilePrint["w.dat"]
0.
0.0008398150100260654
0.0013588492304845074
0.0013588492304845074
0.0008398150100260655
1.7497491811730056*^-19

My question is how it is possible to modify the output of w that:

1. all the results have the same number of digits and

2. to rewrite the result to ...E-19 instead of ...*^-19.

Thank you guys in advance!

Answer 1

Update

Control the number of digits

format[number_, digits_ : 4] :=
 StringReplace[
  TextString[
   EngineeringForm[number, digits, ExponentFunction -> (If[-10 < # < 10, Null, #] &)]],
  {".*10^" -> "E", "*10^" -> "E"}]

Table[format[w[x]], {x, 0, 1, .2}]
(* {"0.", "0.0008398", "0.001359", "0.001359", "0.0008398", "1.75E-19"} *)

Table[format[w[x], 3], {x, 0, 1, .2}]
(* {"0.", "0.00084", "0.00136", "0.00136", "0.00084", "1.75E-19"} *)

---

Here is one way to do it

data = Table[StringReplace[ToString@FortranForm@w[x], "e" -> "E"], {x, 0, 1, .2}]
Export["data.dat", data, "Text"]

You might also want to replace 3.14159 with Pi.