程序代码：

int func (char* str, int c)
{
    int len;
    int count;
    int i;

    len = strlen (str);

    if (len % c != 0)
    {
        return -1;
    }

    count = len / c - 1;

    for (i=1; i<=count; i++)
    {
        if (0 != strncmp (str, str+i*c, c))
        {
            return -1;
        }
    }

    return 0;
}