Sort a String in Alphabetic Order

/*
Write a program in C for sort a string in alphabetic order
*/
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void sort_string(char*);

main()
{
char string[100];

printf("Enter some text\n");
gets(string);

sort_string(string);
printf("%s\n", string);

return 0;
}

void sort_string(char *s)
{
int c, d = 0, length;
char *pointer, *result, ch;

length = strlen(s);

result = (char*)malloc(length+1);

pointer = s;

for ( ch = 'a' ; ch <= 'z' ; ch++ )
{
for ( c = 0 ; c < length ; c++ )
{
if ( *pointer == ch )
{
*(result+d) = *pointer;
d++;
}
pointer++;
}
pointer = s;
}
*(result+d) = '\0';

strcpy(s, result);
free(result);
}