spaja dva stringa sa _

#include <stdio.h>
#include <stdlib.h>

char *spoji (char* p1, char* p2)
{
    char* s=p1;
    while (*s!='\0')
        s++;
    *s='_';
    s++;
    while (*p2!='\0')
         {*s=*p2;
    s++;
     p2++;
}
*s=*p2;
return p1;
}
int main ()
{
    char string1[10], string2[10];
    printf("unesite 2 rijeci: ");
    scanf("%s %s", string1, string2);
     printf ("%s", spoji(string1, string2));
    return 0;
}