[C++] My first IT course with simple output

[Silicon Waffle]

Hi, my C++ course has started since last week and I am learning basic input and output.
In my simple project, I have a function that will return a double number like this

double getLong(long long ll)
{
    return ll/10.00;
}

The input is 12345 and the return value after the code is executed is 1234.500000
I find it strange as to why 0's are added unexpectedly.
I create a console application and test again with main like this

int main()
{
    count<<12345/10.00;
}

But the result becomes 1234.5 which is correct.

Another case I run with my function is if I input e.g 1234567890 then I expect the result should be 123456789.0 (I don't want the compiler to automatically delete my 0 after the decimal point). How can I achieve this ? Thank you a lot.

 

[jedishrfu]

When you print your number count uses a default which escapes me at the moment but which I suspect is a variable format which supresses trailing zeros.

However, you can adjust how numbers are printed:

http://www.arachnoid.com/cpptutor/student3.html

 

[jtbell]

The input is 12345 and the return value after the code is executed is 1234.500000

How do you know what the return value is?

 

[Silicon Waffle]

I see the values in the debugger.
By the way I fixed it using the tutorial link in jedishrfu's post. I learned new thing in C++, setw and set precision. My teacher seemingly forgot them in his previous lecture.
Thanks.

 

[jtbell]

I find it strange as to why 0's are added unexpectedly.

I see the values in the debugger.

The (default) number of decimal places to show is a decision by the authors of the debugger. There might be an option in the debugger's preferences section to change this.

 

[Silicon Waffle]

The (default) number of decimal places to show is a decision by the authors of the debugger. There might be an option in the debugger's preferences section to change this.

Really ? I don't know if there is.

 

[rbelli1]

How exactly is the numerical value 1234.500000 any less correct than 1234.5? Or 1234.500 for that matter?

The output of your program (the text string "1234.5") is what is important and that is correct.

BoB

 

[Silicon Waffle]

How exactly is the numerical value 1234.500000 any less correct than 1234.5? Or 1234.500 for that matter?

The output of your program (the text string "1234.5") is what is important and that is correct.

BoB

Thank you BoB for your insight. Yes, it should be that.
I'm working on a financial application so I need to read from and write to the file the exact values.

 

[D H]

Thank you BoB for your insight. Yes, it should be that.
I'm working on a financial application so I need to read from and write to the file the exact values.

You need to be very careful when using floating point to represent money.

#include <iostream>
int main ()
{
   double x = 0.10;
   double y = 0.20;
   double z = 0.30;
   if ((x+y) != z)
   {  
      std::cout << "This doesn't seem right!\n"
                << x << " + " << y << " - " << z << " = " << x+y-z << '\n';
   }  
}

On most computers, this will print

This doesn't seem right!
0.1 + 0.2 - 0.3 = <some small but non-zero number>

 

[Carno Raar]

The best way to be careful with floating point and currency is not to use floating point for currency.

You can use integers and count cents, or you can look at fixed precision or decimal libraries. If you can't find anything better, there's cpp_dec_float in boost. I believe that in commercial code some juristictions require the use of decimal libraries for currency.