c-gcc, 74 bytes

Result

WA

Code [DL]

f(char*a,char*b){b=*a-*b;}s[100];main(){gets(s);qsort(s,100,1,f);puts(s);}

stdin

6796683867415210874433261120896314080024205986687023144259939265622853102037998115963807234703336894

stdout

4011896766638747152083442360601289431085402206988673221234495939866522153200019798165938037247333869

stderr

/volume/CODE.c:1:1: warning: return type defaults to ‘int’ [-Wimplicit-int]
 f(char*a,char*b){b=*a-*b;}s[100];main(){gets(s);qsort(s,100,1,f);puts(s);}
 ^
/volume/CODE.c: In function ‘f’:
/volume/CODE.c:1:19: warning: assignment makes pointer from integer without a cast [-Wint-conversion]
 f(char*a,char*b){b=*a-*b;}s[100];main(){gets(s);qsort(s,100,1,f);puts(s);}
                   ^
/volume/CODE.c: At top level:
/volume/CODE.c:1:27: warning: data definition has no type or storage class
 f(char*a,char*b){b=*a-*b;}s[100];main(){gets(s);qsort(s,100,1,f);puts(s);}
                           ^
/volume/CODE.c:1:27: warning: type defaults to ‘int’ in declaration of ‘s’ [-Wimplicit-int]
/volume/CODE.c:1:34: warning: return type defaults to ‘int’ [-Wimplicit-int]
 f(char*a,char*b){b=*a-*b;}s[100];main(){gets(s);qsort(s,100,1,f);puts(s);}
                                  ^
/volume/CODE.c: In function ‘main’:
/volume/CODE.c:1:41: warning: implicit declaration of function ‘gets’ [-Wimplicit-function-declaration]
 f(char*a,char*b){b=*a-*b;}s[100];main(){gets(s);qsort(s,100,1,f);puts(s);}
                                         ^
/volume/CODE.c:1:49: warning: implicit declaration of function ‘qsort’ [-Wimplicit-function-declaration]
 f(char*a,char*b){b=*a-*b;}s[100];main(){gets(s);qsort(s,100,1,f);puts(s);}
                                                 ^
/volume/CODE.c:1:66: warning: implicit declaration of function ‘puts’ [-Wimplicit-function-declaration]
 f(char*a,char*b){b=*a-*b;}s[100];main(){gets(s);qsort(s,100,1,f);puts(s);}
                                                                  ^
/volume/CODE.c: In function ‘f’:
/volume/CODE.c:1:1: warning: control reaches end of non-void function [-Wreturn-type]
 f(char*a,char*b){b=*a-*b;}s[100];main(){gets(s);qsort(s,100,1,f);puts(s);}
 ^
/tmp/ccwV2YkV.o: In function `main':
CODE.c:(.text.startup+0xc): warning: the `gets' function is dangerous and should not be used.

strace