A Simple C++ Program

Let’s walk through the steps to create a simple C++ program that will calculate a circle’s area using the formula area = pi x r2

First we’ll set up our preprocessor directives, and an empty main function.

#include <iostream>
using namespace std;

int main() {
}

Next we will need to define variables that will be used by the program. In C/C++ we must define the type of data we are using, along with the variable name. The data type is specified first, then the variable name.

If we define a variable outside of a function, then it is a global variable, and that should be avoided. Instead, define them inside of the function.

double radius;
double area;

For simplicity sake, we will define the variable’s value, instead of reading it in at this time.

radius = 20;

For multiplication, like with almost every language, we use the * (star/asterisk) .

area = radius * radius * 3.14159;

And finally print this data out.

cout << "The area of the circle is: " << area;

With the final program looking like:

#include <iostream>
using namespace std;

int main() {
  double radius;
  double area;

  radius = 20;

  area = radius * radius * 3.14159;

  cout << "The area of the circle is: " << area;

  return 0;
}

A Simple C++ Program was originally found on Access 2 Learn