Jelly, 3 bytes

>ŻY

A full program that accepts a non-negative integer, \$x\$, and prints \$x\$ ones followed by a zero.

Try it online!

Jelly, 3 bytes

>ŻY

A full program that accepts a (non-negative^*) integer, \$x\$, and prints \$x\$ ones followed by a zero.

^{* negative integers will do the same as zero.}

Try it online!

How?

>ŻY - Main Link: non-negative integer, X   e.g. 0      3
 Ż  - zero range                                [0]    [0,1,2,3]
>   - {X} greater than {that}?                  [0]    [1,1,1,0]
  Y - join with newline characters
    - implicit, smashing print