Hehe, funny task.
Code:
void alex()
{
printf(" 0\r");
}
It simply prints a space for the digit 3 that will be printed later in main() and also prints the zero that is missing to form output "30". "\r" returns carriage to the beginning of the line so that the digit 3 is printed instead of the space.{
printf(" 0\r");
}
That doesn't work in Linux console. The carriage return erases the previous characters.
Likewise, alternatively using the "\b" backspace does the same erasing.
At least I didn't need to #include another header file like the accepted solution.
