字符串中的字母大小写转换、生成随机字符串

void lowerToupper(char *str)
{
    while(*str)
    {
        if(*str >= ‘a‘ && *str <= ‘z‘)
        {
            *str -= 32;
        }
        str++;
    }
    *str = ‘\0‘;
}

void upperTolower(char *str)
{
    while(*str)
    {
        if(*str >= ‘A‘ && *str <= ‘Z‘)
        {
            *str += 32;
        }
        str++;
    }
    *str = ‘\0‘;
}

const unsigned char allChar[63] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

void generateStr(char *dest, unsigned int len)
{
    unsigned int cnt, randNo;
    srand((unsigned int)time(NULL));

    for(cnt = 0; cnt < len; cnt++)
    {
        randNo = rand() % 62;
        *dest = allChar[randNo];
        dest++;
    }
    *dest = ‘\0‘;
}