A Variable, in programming, is a symbolic name associated with a location in the computer's memory that is used to store a piece of data. It can be thought of as a labeled container or box where a value can be placed. The value stored in a variable can be changed or "varied" during the program's execution. For example, a programmer can create a variable named voltage_setting and initially assign it a value of 5.0. Later in the program, the same variable can be updated with a new value, such as 10.0. This ability to store and modify data is fundamental to programming.
Before using a variable in many languages (like C++, C#, and Java), it must be "declared," which means giving it a name and specifying its data type (e.g., integer, floating-point number, string). This tells the computer what kind of data the variable will hold and how much memory to allocate for it. Variables are used to store everything from user input and calculation results to the status and measurement readings from a programmable power supply. The opposite of a variable is a constant, which is a value that is fixed when the program starts and cannot be changed.