Maybe being explicit here will help. So,
proc scanf*(fmt: cstring): int {.importc, varargs.}
var a, b, c: cint
echo scanf("%d %d %d", a.addr, b.addr, c.addr) # 3
echo a # first 3 cints that
echo b # user put into stdin
echo c
Run
Save the above in a file called `scan.nim`. Then
echo 1 2 3 | nim r scan
Run
produces four lines (`"3\n1\n2\n3\n"`) while
echo a b c | nim r scan
Run
produces four lines of zeros (`"0\n0\n0\n0\n"`) since "a" etc. do not parse as
decimal integers and since Nim inits them to zero by default (unless you tag
the names with the `{.noInit.}` pragma or give them some other default).
This said, you should also know that the Nim std lib has `std/strscans` which
is nicer in many ways except for porting legacy input parsing:
<https://nim-lang.org/docs/strscans.html>
