c++ different basics types during converting variables

Question

c++ problem different basics types during converting variables Yes, stupid problem, but I'm newbie in c++ and IDK what's the problem.

I have this code:

#include <iostream>
using namespace std;
int main()
{
float a = 54;
cout << a;
double(a);
cout << a;
return 0;
}

and this errors:

error C2371: 'a' : redefinition; different basic types line 7
error C2088: '<<' : illegal for class line 8

why it wrote: different basics types, when I converting only float to double? and what does it mean second error? what class line?

and I have this question too: Can I convert 2 variables with different basic types f.e. int to string? and is it same as converting f.e. double to float or different?

Here is print screen during debugging project in VC++ 2010

[Get yourself a good C++ book](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) — Mooing Duck, Feb 28 '12 at 20:11
Unrelated: The full error messages for Visual Studio are in the "output" window, not the "error" window. — Mooing Duck, Feb 28 '12 at 20:11

mwigdahl · Accepted Answer · 2012-02-28T21:18:24.047

0

You've already declared 'a' as a float, and the compiler thinks you're trying to redeclare it as a double. Try this:

#include <iostream>
using namespace std;
int main()
{
    float a = 54;
    cout << a;
    double b(a);
    cout << b;
    return 0;
}

As far as your second question goes:

Can I convert 2 variables with different basic types f.e. int to string? and is it same as converting f.e. double to float or different?

The answer is that you cannot convert them implicitly or even directly (and have them preserve their meaning, that is), but you can certainly use facilities such as std::stringstream, etc. to do the conversion for you. Conversion from float to double, on the other hand, is an implicit conversion that the compiler will do for you.

edited Feb 28 '12 at 21:18

answered Feb 28 '12 at 18:56

mwigdahl

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gah, I just remembered on the easier solution. How I can check if user written input **int** type? – Cehppel Feb 28 '12 at 19:15
@mwingdahl: I don't think we should recommend `sprintf` for conversion in C++, use `std::stringstream` or `boost::lexical_cast` – Mooing Duck Feb 28 '12 at 20:09
@Cehppel: That is a completely different question, and requires it's own page. – Mooing Duck Feb 28 '12 at 20:10
@MooingDuck: Good point! My C roots are showing, apparently! :) Edited. – mwigdahl Feb 28 '12 at 21:18
ok, I will create new topic, if my try fails. thanks for all advices – Cehppel Feb 29 '12 at 11:14
I found this: http://stackoverflow.com/questions/4049549/c-number-input-validation and it's ok! – Cehppel Feb 29 '12 at 11:22

c++ different basics types during converting variables

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