# C - 64 characters, 64 points

    main(int a,char**b){b++;qsort(*b,strlen(*b),1,strcmp);puts(*b);}

You might wonder how I get this to work without any headers.  Simple, compile with:

    gcc -include stdio.h stdlib.h string.h test.c -o test --std=gnu11 -Wall -g -O3

**Un-golfed:**

    #include <stdio.h> 
    #include <stdlib.h>
    #include <string.h>
    
    main(int a, char **b)
    {
        b++;
    	qsort(*b, strlen(*b), sizeof(char), strcmp);  // sizeof(char) is guaranteed to be 1 by standards
    	puts(*b);
    }

---

I also decided to include sorting of characters, just because I could.

Test runs:

    $ ./test 132815
    112358
    $ ./test 423791
    123479
    $ ./test 1234767189728975213132471243985123957120837412
    0111111112222222233333344445556777777788889999
    $ ./test 4789359uihjasvb8ygohq9poi3n4jiouy58g
    3344557888999abgghhiiijjnooopqsuuvyy