Bubble-sort C

[mason64]

rite a function that when invoked as bubble_string(s) causes the characters in the string s to be bubble-sorted. If s contains the string "xylophone", then the following statement should cause ehlnoopxy to be printed.
The errors I get are: 10.4.c: In function `main':
10.4.c:8: error: invalid use of void expression
10.4.c: In function `bubble_string':
10.4.c:17: error: syntax error before ')' token
Any ideas on how to fix this?

#include <stdio.h>
void swap (char*, char*);
void bubble_string(char s[]);

int main(void)
{
        char *s= "xylophone";
        printf("%s", bubble_string(s));

return 0;
}

void bubble_string(char s[])
{
        char i, j, n;
        n  = strlen(s);
        for(i = 0)
                for(j = n - 1)
                        if(s[j-1] > s[j])
                                swap(&s[j-1], &s[j]);
}

[CommonTater]

Your for() statements are incorrectly composed... look it up in you C library documentation.
The swap() function is declared but never defined.
You should not pass your string s into bubble_string() as an array, use a pointer (char *s) instead.