I already don't know what to do, because I think that my prog works okay for all possible and impossible test cases. Please, consider the source code: (If the 'ended' logical principle is removed, it fails on the 2nd test)

int main(void)
{
    int i, ended = 1;
    char last, blonde[MAXBUF];

    while (gets(blonde)) {
        if (!blonde[0]) continue;

        for (i = 0; !isalpha(blonde[i]); i++)
            ;
        if (!ended) blonde[i] = tolower(blonde[i]);
        else        blonde[i] = toupper(blonde[i]);

        for (++i; blonde[i] != '\0'; i++) {
            if (isalpha(blonde[i]))
                blonde[i] = tolower(blonde[i]);
            else if (blonde[i] == '.' || blonde[i] == '!' || blonde[i] == '?') {
                while (!isalpha(blonde[++i]))
                    ;
                blonde[i] = toupper(blonde[i]);
            }
        }
        puts(blonde);
        last = strlen(blonde) - 1;
        if (blonde[last] == '.' || blonde[last] == '!' || blonde[last] == '?')
           ended = 1;
        else
           ended = 0;
    }
    return 0;
}