Processing a double variable as boolean

Question

What is the best way (efficiency / best practice) to check if a double variable is equal to 0?

    1. if(a_double)
          .....
       else
          .....

    OR

    2. if(a_double == 0)
          .....
       else
          .....

Answer 1

The second is usually better (in more detail about what you are doing). I usually prefer if (a_double == 0.0). Also note that floating-point approximation comparisons are often useful given the possibility of rounding in calculations (although doing this well may be nontrivial).

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Answer 2

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: http://docs.sun.com/source/806-3568/ncg_goldberg.html

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Answer 3

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#include<iostream>
using namespace std;
int main(){
double a=3/5;
double b=2/5;
double c=(a+b)-1;
if(c==0)
        cout<<"C is 0"<<endl;
else if(c==0.0)
        cout<<"C is 0.0"<<endl;
else
        cout<<"C!=0 && C!=0.0"<<endl; //This will print most of the time
}

- -

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#include<iostream>
using namespace std;
int main(){
double a=5.5;
double b=6.5;
double c=(a+b)/12;
if(c==0)
        cout<<c<<endl;
else
        cout<<"c is not equal to 0"<<endl;
}