C++ Type Conversion during Arithmetic Operation

Question

I am new to programming and learning C++ using C++ Primer Plus, 6th Ed. by Stephen Prata.

In Chapter 3, it states that

"when an operation involves two types, the smaller is converted to the larger."

The example it provides is from a previous listing where 9.0/5 (double divided by int) results in a value of 1.8 (double). It states that 5 is converted to double before doing the division. Hence, a double divided by a double will result in a value that is also double. This makes sense.

However, if this is the case, why is it that 10.0 / 5 (double divided by int) results in 2 (int). Should not the answer be 2.0 (if 5 is converted to double and then divided into 10.0)?

What makes you think 10.0 / 5 gives an integer result ? It doesn't. — Paul R, Feb 12 '15 at 21:45
um… The result of `10.0 / 5` is of type `double`. It definitely is. It's also `2.0` if you print it appropriately. Is this just a printing issue maybe? — The Paramagnetic Croissant, Feb 12 '15 at 21:45
Also consider using a [better book](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list). — Paul R, Feb 12 '15 at 21:46
Thanks! I looked at various reviews and think I will start on C++ Primer. However, I will still use some of the problems from C++ Primer Plus, etc. — Pranjal Manchanda, Feb 12 '15 at 22:57

score 1 · Answer 1 · answered Feb 12 '15 at 21:47

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When you print a double with .0, the output is just the integer part. You can test it by compiling this code:

double num = 2.0;
std::cout << num;

Output will be: 2

answered Feb 12 '15 at 21:47

Michael

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Thanks! That is exactly what I was wanting an answer to! – Pranjal Manchanda Feb 12 '15 at 21:50
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Note that you can change the way std::cout prints doubles and make it print `2.0`. You can use std::setprecision(int), however std::cout is not the only way to print something. – Michael Feb 12 '15 at 22:03
@Michael are you suggesting to use `printf()`? this is no longer C++, though. – Walter Feb 12 '15 at 22:07
@Walter no I didn't. qDebug() should print doubles as `2.0` for debugging purposes but I'm not sure. – Michael Feb 12 '15 at 22:17

score 0 · Answer 2 · answered Feb 12 '15 at 22:07

0

"when an operation involves two types, the smaller is converted to the larger."

The book's citation doesn't refer to the values of the types used in an operation, but their size.

answered Feb 12 '15 at 22:07

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C++ Type Conversion during Arithmetic Operation

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