Two limited scope variables vs one global

The answer to the question of whether to use two limited scope variables or one global variable is neither. Pi is a constant, not a variable, and is defined in <numbers> in C++20, or commonly by M_PI in <math.h> / <cmath> (requires _USE_MATH_DEFINES in VC++, but not gnu or clang).

Here are some reasons why using a constant is better than using a variable:

• Constants cannot be changed, which helps to prevent errors.
• Constants are more readable and easier to understand than variables.
• Constants can be used in more places than variables, such as in expressions and as arguments to functions.

If you need to use a value that is not a constant, then you can use a variable. However, you should always try to use a constant whenever possible.

Here is an example of how you can use a constant in C++:

```cpp #include using namespace std; int main() { // Declare a constant named pi. const double pi = numbers::pi; // Use the constant pi in a calculation. double area = pi * radius * radius; // Print the result of the calculation. cout << "The area of the circle is " << area << " square units." << endl; return 0; } ```

In this example, the constant pi is used to calculate the area of a circle. The constant pi cannot be changed, which helps to prevent errors. The constant pi is also more readable and easier to understand than a variable.