I am trying to make a rounding function

Projects Programming
3

I doubt that that if structure is doing what you think. The comma does not belong in an if structure. Maybe && (logical and) is what you need there instead.

Try this with some different numbers:

int number = 450;

void setup()
{
   Serial.begin(115200);
   int tempNumber = number / 100;
   tempNumber = tempNumber * 100;
   Serial.println(tempNumber);
}

void loop()
{
}

Thanks for posting code properly on your first post. Few first time posters bother to read the guidelines. Good job.