#include<iostream.h>
int main()
{
    float r,d,c,a;
    const float pi = 3.14159;
    cout<<" Enter the value of radius : ?\b";
    cin>>r;
    d = r * 2;
    c = 2 * pi * r;
    a = pi * r * r;
    cout<<" Diameter :  "<<d<<endl;
    cout<<" Circumference:  "<<c<<endl;
    cout<<" Area :  "<<a<<endl;
    return 0;
}

Output:
Enter the value of radius : 2.45
Diameter :  4.9
Circumference:  15.3938
Area :  18.8574
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