## How to find the volume of a cylinder:

In this post, we will learn learn how to find the *volume* of a cylinder with user input values. The formula we need to find the cylinder volume is *π r^2h*, where

*r*is the radius of the cylinder,

*h*is the height of the cylinder, and

*π*is the mathematical constant

*PI*.

Since *π* is a constant value, we need the radius and height of a cylinder to calculate its *volume*. The program will take these values as inputs from the user, calculate the volume and print it out.

### Method 1: C++ program to find the volume of a cylinder:

The below program calculates the *volume* of a cylinder:

```
#include <iostream>
using namespace std;
int main()
{
double height, radius, volume;
double PI = 3.14159;
cout << "Enter the height of the cylinder: " << endl;
cin >> height;
cout << "Enter the radius of the cylinder: " << endl;
cin >> radius;
volume = PI * radius * radius * height;
cout << "The volume of the cylinder is: " << volume << endl;
}
```

Here,

- The
*height*,*radius*and*volume*are three double variables to hold the height, radius and volume of the cylinder. *PI*is a double value to hold the value of*π*.- It asks the user to enter the
*height*and*radius*of the cylinder. It reads the user input values and assigns these to the*height*and*radius*variables. - The calculated volume value is assigned to the
*volume*variable and the last line prints its value.

If you run this program, it will print output as like below:

```
Enter the height of the cylinder:
33
Enter the radius of the cylinder:
5
The volume of the cylinder is: 2591.81
Enter the height of the cylinder:
32
Enter the radius of the cylinder:
22
The volume of the cylinder is: 48656.9
```

### Method 2: C++ program to find the volume of a cylinder using predefined PI value:

In the above example, we used the *π* value from a predefined constant. It’s value is already defined in the *cmath* header file. Let’s learn how to use this value from *cmath* in the below example:

```
#include <iostream>
#include <cmath>
using namespace std;
int main()
{
double height, radius, volume;
cout << "Enter the height of the cylinder: " << endl;
cin >> height;
cout << "Enter the radius of the cylinder: " << endl;
cin >> radius;
volume = M_PI * radius * radius * height;
cout << "The volume of the cylinder is: " << volume << endl;
}
```

As you can see here,

*cmath*header is included to the start of the program.*M_PI*is the constant that holds the PI value. We are using it to calculate the volume.

Sample output:

```
Enter the height of the cylinder:
100
Enter the radius of the cylinder:
22
The volume of the cylinder is: 152053
```

### Method 3: C++ program to find the volume of a cylinder using a separate function:

Let’s use a separate function to calculate the *volume* of the cylinder. This method will be called from *main()* or any other method and it will calculate and return the volume.

```
#include <iostream>
#include <cmath>
using namespace std;
double getVolume(double radius, double height)
{
return M_PI * radius * radius * height;
}
int main()
{
double height, radius, volume;
cout << "Enter the height of the cylinder: " << endl;
cin >> height;
cout << "Enter the radius of the cylinder: " << endl;
cin >> radius;
volume = getVolume(radius, height);
cout << "The volume of the cylinder is: " << volume << endl;
}
```

Here,

*getVolume*function calculates the volume. It takes the*radius*and*height*of the cylinder as parameters and returns the calculated volume.- The returned value is assigned to the double value
*volume*in the main function.

You will get similar results.

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