Hey guys I was writting a program when I came up with a problem I couldn't explain.

Here is my questionable part of code, i include only whats needed.

Before writing the code as seen (working now)
What i wrote was minthr=maxhr*(50/100);
maxthr=maxhr*(85/100);

Printf results were zeroes.

Why was there such a problem using parenthesis?

Good question.

First, the arithmetic is done from left to right.
So if maxhr was 90, in the statement would first do 90*50 and then 4500/100.
The answer to that would be 45.

If you were to use the parentheses as you show you would first do the (50/100).
In C that would return an int - a whole number with no fraction.
ie: the number of times 100 goes into 50, which is zero.
And of course maxhr*0 will always return 0.

To get that to return a fraction you can simply introduce an decimal point like this:
This is called 'casting' from one type to another. (from type int to type double)
In C this is done automatically according to what type is requested as the statement is processed as determined by order of precedence.

You can also specify a type in your code. (casting). So you want to review operators '/' and '%' and "operator precedence" and "data casting" in your book.

It's a bit confusing at first but you'll get used to it.

Oh, I see. Thank you!