Why does division result in zero instead of a decimal?

Teaching myself C and finding that when I do an equation for a temp conversion it won't work unless I change the fraction to a decimal. ie,

tempC=(.555*(tempF-32)) will work but tempC=((5/9)*(tempF-32)) won't work.

Why?
According to the book "C Primer Plus" it should work as I'm using floats for both tempC and tempF.

Solution 1:

It looks like you have integer division in the second case:

tempC=((5/9)*(tempF-32))

The 5 / 9 will get truncated to zero.

To fix that, you need to make one of them a floating-point type:

tempC=((5./9.)*(tempF-32))

Solution 2:

When you do 5/9, 5 and 9 are both integers and integer division happens. The result of integer division is an integer and it is the quotient of the two operands. So, the quotient in case of 5/9 is 0 and since you multiply by 0, tempC comes out to be 0. In order to not have integer division, atleast one of the two operands must be float.

E.g. if you use 5.0/9 or 5/9.0 or 5.0/9.0, it will work as expected.

Solution 3:

5/9 is an integer division not a floating point division. That's why you are getting wrong result.

Make 5 or 9 floating point variable and you will get correct answer.

Like 5.0/9 OR 5/9.0

Solution 4:

5/9 is an integer expression, as such it gets truncated to 0. your compiler should warn you about this, else you should look into enabling warnings.