Why can't I get a decimal number in C++?

So there's a question in my textbook.

number = (1/3) * 3;

cout << "(1/3) * 3 is equal to " << number;

the answer should be 0.99999...

While in the C++,

when I declared the variable number as integer. The output answer is 0. I got it because it won't calculate the decimal unless I told the program.

So I declared it again as double. The output is 1.

Then, I changed 1/3 to 1.0/3. (my textbook said if one number is int and another number is double, the output will be double )

However, my output is still 1.

Then, I declared it as double and changed the whole as (1.0/3.0)*3.0

The answer is still 1.

How can I get the 0.9999999999999... or 0.9(at least it approximate than 1)