Question

I am learning C++ in 11th standard. I don’t have much knowledge about C++

In my college, there is visual studio 2005. I have a project to convert celsius to farenheit. This code works fine in my college in visual studio 2005:

#include <iostream>

int main()
{
   float f,cs;

    cin>>cs;
    cout<<"\n celsius = "<<cs;
    f=1.8*cs+32.0;
    cout<<"f = "<<f;
}

But when I run this code in visual studio 2012 after modifying:

#include "stdafx.h"
#include <iostream>
using namespace std;

int main()
{
   float f,cs;

   cin>>cs;
   cout<<"\n cs = "<<cs;
   f=1.8*cs+32.0;
   cout<<"f = "<<f;
}

It gives me following errors:

conversion from double to float possible

Answer 1

You are getting a warning, as you multiply 1.8 (which is a double literal) with cs, yielding a double. In C++, if you have an expression with two different types, a type promotion is performed to the type with the largest value range; for double and float this means that cs is converted to double. This is then assigned to a float, which might not be able to represent the full value range of double (float is a 32-bit IEEE floating point number, double is 64-bit.) Hence the warning.

You can fix this by writing:

f=1.8f*cs+32.0f;

or by changing f to be of type double.

Note: Your code is compiling, this is just a warning, not an error.