为什么我们不能将运算符与浮点数一起使用？

Question

What's wrong to use operators while you are using floating point numbers. Can't we use '==' '<=' etc operators with floating point numbers?

here is the code.

# include <iostream>

using namespace std;

main(){
 float x, y, z;
 cout<<"1st integer: ";
 cin>>x;

 do {
    cout<<"2nd integer: ";
    cin>>y;
    if(y<=0 ){
            cout<<"You can't divide by zero"<<endl;
            continue;
        } else {
                break;
                }
        } while (1);

z = x/y;
cout<<"Result: "<<z;


}

it generate right result as i want to get. But from some where i heard that's not a good logic to use operators with floating point numbers. why?

Answer 1

What you're doing is fine. What you do need to be wary of is using the equality operator == with floating point, because the results may surprise you (eg 0.1 + 0.2 != 0.3 ).

But there's no problem with using > , >= , <= , < .

Answer 2

You can compare floating point numbers safely against precisely zero. This will prevent a division by zero.

What you can't do is check x==0.1 and then divide by x-0.1 . Since 0.1 isn't exactly representable, you have rounding in a generally unknown direction.