Warning converting to `int' from `double' - c++

Question

Hey this is really one of the first things I've ever coded. I was wondering how might I fix this error. I am currently trying to do some research but can't find anything that is helpful in fixing it.
#include <iostream> // needed for Cin and Cout
#include <cmath>
#include <csmath>
using namespace std;
/************************************
* defines
*************************************/
#define PI 3.14159
/*************************************
* function prototype
*************************************/
int main()
{
//surface and volume
float radius;
float height;
float surfacearea;
float volume;
int pi = 3.14159
//Get the radius
cout << "enter the radius: ";
cin >> (float)radius;
//Get height
cout << "enter height: ";
cin >> height;
//Get the surfacearea
surfacearea = 2(pi*radius^2)+2(pi*radius)* height;
cout << "The surfacearea is: " << surfacearea;
//get volume
volume = (pi*radius)^2*height;
cout << "The volume is: " << volume << endl;
system ("pause");
return 0;
}

Answer 1

Change int to double for pi, because pi is a floating point number, which, as stated in the comments, is C++'s default for floating point numbers. Unless there is a particular reason to use float, use double for floating-point numbers.
double pi = 3.14159;
And the warning will go away.
Also, you don't have to cast your input to float, simply:
cin >> radius;
Additionally, at the very least, change radius^2 to radius*radius.
But better yet, avoid ^ altogether and use std::pow, an example of which can be found here.
Additionally, you don't need to #define PI 3.14159 because you never use it, and you try to define pi in main().

Answer 2

You better declare and initialize local variables right before you need them. For constants like pi you better use const and proper type. For a proper type C++11 offers you a great tool - auto. And ^ does not mean power in C++ you have to use std::pow() instead. So your code should look like this:
const auto pi = 3.14159;
//Get the radius
auto radius = 0.0;
cout << "enter the radius: ";
cin >> radius;
//Get height
auto height = 0.0;
cout << "enter height: ";
cin >> height;
//Get the surfacearea
auto surfacearea = 2 * pi * pow( radius, 2.0 ) + 2 * pi * radius * height;
cout << "The surfacearea is: " << surfacearea << endl;
//get volume
auto volume = pow( pi*radius, 2.0 ) * height;
cout << "The volume is: " << volume << endl;

Answer 3

To begin with, a warning is not an error; if it were a compilation error, then the code would not even compile. However, since it was a warning, that means your code did compile successfully and run, except that it produced a warning about something in your code. Now to the bugs in your code:
Firstly, your declaration for the local variable pi is incorrect. pi is declared in your code as a variable of data type int, short for integer. An integer is only a whole number, positive and negative one, but one that is neve more specific than 10^0. Now the problem is that you are trying to store a decimal value in an int variable. While the compiler is able to make a conversion of the decimal value into an int value, you lose the precision of the value; that's because it rounds the value. If you compile this sample code:
int floating = 1.23456789;
cout << floating << endl;
It will output 1 instead of 1.23456789, with the reason being that an int variable cannot store a float or double value; it however can convert this float or double value into an int value by rounding it.
Therfore, you should change your declaration for pi to:
double pi = 3.14159; // By the way, you forgot to add a semicolon here
Another problem: you are using unnecessary typecating in your cin statement for the radius:
cin >> (float)radius;
You would need to use casting if you want to change the data type of a variable for a particular operation (you don't change the variable data type; you merely process its value as the data type cast. In your case, it is unrequired, because the radius variable is already declared as a data type of float, in the line:
float radius;
Therefore, I would recommend you to simply change this cin statement to:
cin >> radius;
One more thing: the following lines in your code have a problem:
surfacearea = 2(pi*radius^2)+2(pi*radius)* height;
volume = (pi*radius)^2*height;
The "^" symbol does not raise a number to a power; it is called a bitwise XOR operator in c++ and it server the purpose of copying the bit if it is set in one operand but not both. You can find more information about it here: Bitwise Exclusive OR Operator: ^
In c++, if you want to raise a number x to a power like 2, then you have to do x * x. Alternatively, you can use the pow() function like: pow(x, 2.0). For your code, if we use the x*x method, it would be like:
surfacearea = 2(pi*radius*radius)+2(pi*radius)* height;
volume = (pi*radius)*(pi*radius)*height;
Alternatively, if we use the pow() function, then the code would look like:
surfacearea = 2(pi*pow(radius, 2))+2(pi*radius)* height;
volume = pow((pi*radius), 2)*height;
Fixing these peoblems should get your code to work.