Mathematica, 48 47 46 bytes

-1 byte thanks to Martin Ender!

StringLength[""<>ToString/@Range[0,#,Sign@#]]&

Anonymous function, taking the number as an argument.

###Shorter solution by Greg Martin, 39 bytes

1-#~Min~0+Tr@IntegerLength@Range@Abs@#&

Mathematica, 48 47 46 bytes

-1 byte thanks to Martin Ender!

StringLength[""<>ToString/@Range[0,#,Sign@#]]&

Anonymous function, taking the number as an argument.

Shorter solution by Greg Martin, 39 bytes

1-#~Min~0+Tr@IntegerLength@Range@Abs@#&

Mathematica, 48 47 46 bytes

-1 bytes thanks to @MartinEnder!

StringLength[""<>ToString/@Range[0,#,Sign@#]]&

Anonymous function, taking the number as an argument.

###Shorter solution by @GregMartin, 39 bytes

1-#~Min~0+Tr@IntegerLength@Range@Abs@#&

Mathematica, 48 47 46 bytes

-1 byte thanks to Martin Ender!

StringLength[""<>ToString/@Range[0,#,Sign@#]]&

Anonymous function, taking the number as an argument.

###Shorter solution by Greg Martin, 39 bytes

1-#~Min~0+Tr@IntegerLength@Range@Abs@#&

Mathematica, 48 47 46 bytes

-1 bytes thanks to @MartinEnder!

StringLength[""<>ToString/@Range[0,#,Sign@#]]&

Anonymous function, taking the number as an argument.

Mathematica, 48 47 46 bytes

-1 bytes thanks to @MartinEnder!

StringLength[""<>ToString/@Range[0,#,Sign@#]]&

Anonymous function, taking the number as an argument.

###Shorter solution by @GregMartin, 39 bytes

1-#~Min~0+Tr@IntegerLength@Range@Abs@#&