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A constant is a data item whose value cannot change during the course of program execution.
A variable is a data item whose value can vary during the course of program execution.
Variables and parameters are widely used in fields like physics, statistics, mathematics, and analysis. However, they are often misunderstood as the same entity.
Variables
A variable is a data item whose value can change during a program’s execution. Variables are used in a variety of ways throughout a program.
One of the most common ways to use a variable is to store a piece of information in it. This can be a number, string, or other type of information.
However, sometimes you don’t want to update this information anywhere in the program. You can make a constant variable by initializing it at the very beginning of the program.
When a variable is first declared, it has a name and type. The name identifies the location in memory where this information is stored, and the type explains what kind of data is stored with the variable.
Constants
A constant is a data item that cannot change during the program’s execution. It’s the opposite of a variable, which allows you to access its value but also to reassign it.
Constants are used in many programming situations. They can represent physics or mathematical constants that don’t change (such as pi, Avogadro’s number), or application-specific “tuning” values, like friction or gravity coefficients.
One of the best ways to handle these constants is to define them together with the code that uses them. This can help to ensure that they don’t get out of sync and cause errors. You can do this by defining them as superglobals or by using inline variables, for example. Another helpful strategy is to define them as system variables on Windows or environment variables on macOS and Linux. This helps keep them from cluttering your project files. Regardless of the strategy you choose, remember to assign them a value when they’re defined so that you don’t run into compilation errors.
Parameters
A parameter is a workbook variable like a number, date, or calculated field that allows users to replace a constant value in a calculation, filter, or reference line.
Parameters are also used in some programming languages. They are passed into a function to identify its values and can be called from within that function or subroutine.
For example, a general equation that has m and b as parameters is called a parametric equation. The set of solutions (x, y) to that equation describes the curve of a plane.
In statistics, a parameter is a variable whose value is sought using evidence from samples. The resulting assigned value is the estimate, or statistic. Examples of statistics or parameters include the mean, standard deviation, and population mean.
Examples
A constant variable is a value that does not change over time. This type of value can be useful for representing quantities, magnitudes, objects, parameters, or any other piece of data that’s supposed to remain the same for an extended period of time.
Constants are also valuable for preventing errors that can occur when you write a value repeatedly in different parts of your code. For example, when you want to increase the precision of a number, it can be annoying to have to manually change it in each place where it appears.
The best way to avoid this problem is to use a named constant instead of writing a value in each method. This can make your code more reliable, maintainable, and readable.