Convert int to string with leading zeros

Question

I have an integer which I want to convert to a string with leading zeros.

So I have 1 and want to turn it into 01. 14 should turn into 14 not 014.

I tried:

let str = (string 1).PadLeft(2, '0') // visual studio suggested this one
let str = (string 1).PadLeft 2 '0'
let str = String.PadLeft 2 '0' (string 1)

But neither work :( When I search for something like this with F# I get stuff with printfn but I don't want to print to stdout :/

Disclaimer: This is my first F#

score 23 · Accepted Answer · answered Nov 01 '16 at 14:34

23

You can use sprintf which returns a string rather than printing to stdout. Any of the print functions that start with an s return a string.

Use %0i to pad with zeroes. Add the length of the intended string between 0 and i. For example, to pad to four zeroes, you can use:

sprintf "%04i" 42

// returns "0042"

answered Nov 01 '16 at 14:34

Chad Gilbert

I totally missed the part with `s` in front of `print` :) – Snæbjørn Nov 01 '16 at 14:39
For some reason `%0i` doesn't work but `%02i` works like a charm – Snæbjørn Nov 01 '16 at 14:41
2

@Snæbjørn, `%0i` makes no sense because in order to zero-pad a string, you need to know to what length it should be padded. – Be Brave Be Like Ukraine Nov 01 '16 at 15:13
How would I pad the string from a function param? `sprintf "%0[dynamic int param]i" 42`. – Jecoms Sep 30 '19 at 18:49
@Jecoms - to pad a variable number of characters you can use [String.PadLeft(...)](https://learn.microsoft.com/en-us/dotnet/api/system.string.padleft) as in `(string 42).PadLeft(4, '0')` – Chad Gilbert Oct 02 '19 at 11:30

1 Answers1