char *copy(char *dest, const char *src, int capacity) {
    for (int i = 0; i < capacity - 1; i++){
            if (src[i] == '\0'){
                    break;
            } else {
                    dest[i] = src[i];
            
    }
    dest[capacity - 1] = '\0';
    return dest;
}

Write the copy function to perform exactly as strncpy does, with one
   exception: your copy function will guarantee that dest is always
   null-terminated. Capacity is expected to be the number of bytes of 
   memory allocated to dest.
   You shoud read the man page to learn how strncpy works.

  NOTE: You must write this function without using any string functions.
  The only function that should depend on string.h is memset.