I can't print a double value in the following code? - c++

Question

#include <iostream>
#include <iomanip>
using namespace std;
double distance(double, double);
int main ()
{
double rate, time, distanceValue;
cout << fixed << showpoint << setprecision(1);
cout << "Enter rate" << endl;
cin >> rate;
cout << "Enter time" << endl;
cin >> time;
distanceValue = distance(rate, time);
cout << "The distance is " << distanceValue << endl;
}
double distance (double num1, double num2)
{
return num1 * num2;
}
when I try to compile it I see a long list of errors I don't what's wrong here! also if I change the method from double to int value it works well!! why??
the following error:
*> C:\Users\kifcaliph\Desktop\starting
out with c++\Chapter6>cl 06_012.cpp
06_012 Microsoft (R) 32-bit C/C++
Optimizing Compiler Version
16.00.30319.01 for 80x86 Copyright (C) Microsoft Corporation. All rights
reserved.
cl : Command line warning D9024 :
unrecognized source file type
'06_012', object file assumed
06_012.cpp C:\Program Files
(x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xlocale(323) : warning C4530: C++ exception handler used,
but unwind semantics are not enabled.
Specify /EHsc C:\Program Files
(x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(373) : error C2825: '_Iter': must be a class or
namespace when followed by '::'
06_012.cpp(20) : see reference to class template instantiation
'std::iterator_traits<_Iter>' being
compiled
with
[
_Iter=double
] C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(373) : error C2039: 'iterator_category' : is not a
member of 'global namespace''
C:\Program Files (x86)\Microsoft
Visual Studio
10.0\VC\INCLUDE\xutility(373) : error C2146: syntax error : missing ';' b
efore identifier 'iterator_category'
C:\Program Files (x86)\Microsoft
Visual Studio
10.0\VC\INCLUDE\xutility(373) : error C2602: 'std::iterator_traits<_Iter>
::iterator_category' is not a member
of a base class of
'std::iterator_traits<_Iter>'
with
[
_Iter=double
]
C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(373) : see declaration of 'std::iterator
_traits<_Iter>::iterator_category'
with
[
_Iter=double
] C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(373) : error C2868: 'std::iterator_traits<_Iter>
::iterator_category' : illegal syntax
for using-declaration; expected
qualified-name
with
[
_Iter=double
] C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(374) : error C2825: '_Iter': must be a class or
namespace when followed by '::'
C:\Program Files (x86)\Microsoft
Visual Studio
10.0\VC\INCLUDE\xutility(374) : error C2039: 'value_type' : is not a memb er
of 'global namespace'' C:\Program
Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(374) : error C2146: syntax error : missing ';' b
efore identifier 'value_type'
C:\Program Files (x86)\Microsoft
Visual Studio
10.0\VC\INCLUDE\xutility(374) : error C2602: 'std::iterator_traits<_Iter>
::value_type' is not a member of a
base class of
'std::iterator_traits<_Iter>'
with
[
_Iter=double
]
C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(374) : see declaration of 'std::iterator
_traits<_Iter>::value_type'
with
[
_Iter=double
] C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(374) : error C2868: 'std::iterator_traits<_Iter>
::value_type' : illegal syntax for
using-declaration; expected
qualified-name
with
[
_Iter=double
] C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(375) : error C2825: '_Iter': must be a class or
namespace when followed by '::'
C:\Program Files (x86)\Microsoft
Visual Studio
10.0\VC\INCLUDE\xutility(375) : error C2039: 'difference_type' : is not a
member of 'global namespace''
C:\Program Files (x86)\Microsoft
Visual Studio
10.0\VC\INCLUDE\xutility(375) : error C2146: syntax error : missing ';' b
efore identifier 'difference_type'
C:\Program Files (x86)\Microsoft
Visual Studio
10.0\VC\INCLUDE\xutility(375) : error C2602: 'std::iterator_traits<_Iter>
::difference_type' is not a member of
a base class of
'std::iterator_traits<_Iter>'
with
[
_Iter=double
]
C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(375) : see declaration of 'std::iterator
_traits<_Iter>::difference_type'
with
[
_Iter=double
] C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(375) : error C2868: 'std::iterator_traits<_Iter>
::difference_type' : illegal syntax
for using-declaration; expected
qualified-name
with
[
_Iter=double
] C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(377) : error C2825: '_Iter': must be a class or
namespace when followed by '::'
C:\Program Files (x86)\Microsoft
Visual Studio
10.0\VC\INCLUDE\xutility(377) : error C2039: 'pointer' : is not a member of
'global namespace'' C:\Program Files
(x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(377) : error C2146: syntax error : missing ';' b
efore identifier 'pointer' C:\Program
Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(377) : error C2602: 'std::iterator_traits<_Iter>
::pointer' is not a member of a base
class of 'std::iterator_traits<_Iter>'
with
[
_Iter=double
]
C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(377) : see declaration of 'std::iterator
_traits<_Iter>::pointer'
with
[
_Iter=double
] C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(377) : error C2868: 'std::iterator_traits<_Iter>
::pointer' : illegal syntax for
using-declaration; expected
qualified-name
with
[
_Iter=double
] C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(378) : error C2825: '_Iter': must be a class or
namespace when followed by '::'
C:\Program Files (x86)\Microsoft
Visual Studio
10.0\VC\INCLUDE\xutility(378) : error C2039: 'reference' : is not a membe r
of '`global namespace'' C:\Program
Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(378) : error C2146: syntax error : missing ';' b
efore identifier 'reference'
C:\Program Files (x86)\Microsoft
Visual Studio
10.0\VC\INCLUDE\xutility(378) : error C2602: 'std::iterator_traits<_Iter>
::reference' is not a member of a base
class of 'std::iterator_traits<_Iter>'
with
[
_Iter=double
]
C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(378) : see declaration of 'std::iterator
_traits<_Iter>::reference'
with
[
_Iter=double
] C:\Program Files (x86)\Microsoft Visual Studio
10.0\VC\INCLUDE\xutility(378) : error C2868: 'std::iterator_traits<_Iter>
::reference' : illegal syntax for
using-declaration; expected
qualified-name
with
[
_Iter=double
]
C:\Users\kifcaliph\Desktop\starting
out with c++\Chapter6>*

Answer 1

I'm guessing (since you didn't bother to actually show us the errors in question) that there's an ambiguity error between std::distance and ::distance that's coming into play because of your using directive. Fully qualify ::distance to force your function to be called, or get rid of the using directive and either fully qualify everything or add a using declaration for each of the symbols inside namespace std that you intend to use.
Also, you misspelled distanceValue as distancValue in the last line of main.

Answer 2

You are seeing an unfortunate side effect of using namespace std;. There is a function called std::distance; since you used using namespace std; it takes precedence over your own distance function.
The solution is to not use using namespace std;, and instead reference std::cout, std::setprecision, etc individually. You can also import specific identifiers from std:
using std::cout;
using std::setprecision;
using std::fixed;
using std::showpoint;
using std::cin;
using std::endl;
Or you can continue using using namespace std;, but explicitly request your own distance with ::distance - this requests distance from the empty namespace specifically (not recommended; if anything is added to std this could break again).
Also, distancValue is a typo.

Answer 3

It'll be ambiguity between std::distance and your ::distance - either fully qualify the call, or dont include the whole of the std namespace.

Answer 4

The error is that you wrote:
cout << "The distance is " << distancValue << endl;
instead of:
cout << "The distance is " << distanceValue << endl;
You see, there is a little 'a' in distance that you missed, fix it and it will work well.
And be careful next time :)