C ++中的浮点变量

Question

I'm learning C++, and encountering these problems in a simple program, so please help me out.

This is the code

#include<iostream>
using std::cout;
int main()
{   float pie;
    pie = (22/7);
    cout<<"The Value of Pi(22/7) is "<< pie<<"\n";
    return 0;
}

and the output is

The Value of Pi(22/7) is 3

Why is the value of Pi not in decimal?

Answer 1

That's because you're doing integer division .

What you want is really float division:

#include<iostream>
using std::cout;
int main()
{   
    float pie;
    pie = float(22)/7;//        22/(float(7)) is also equivalent

    cout<<"The Value of Pi(22/7) is "<< pie<<"\n";
    return 0;
}

However, this type conversion: float(variable) or float(value) isn't type safe.

You could have gotten the value you wanted by ensuring that the values you were computing were floating point to begin with as follows:

22.0/7

OR

22/7.0

OR

22.0/7.0

But, that's generally a hassle and will involve that you keep track of all the types you're working with. Thus, the final and best method involves using static_cast :

static_cast<float>(22)/7 

OR

22/static_cast<float>(7) 

As for why you should use static_cast - see this:

Why use static_cast<int>(x) instead of (int)x?

Answer 2

pie = (22/7);

Here the division is integer division, because both operands are int .

What you intend to do is floating-point division:

pie = (22.0/7);

Here 22.0 is double , so the division becomes floating-point division (even though 7 is still int ).

The rule is that IF both operands are integral type (such as int , long , char etc), then it is integer division, ELSE it is floating-point division (ie when even if a single operand is float or double ).

Answer 3

Use:

      pi = 22/7.0

If u give the two operands to the / operator as integer then the division performed will be integer division and a float will not be the result.