In programming, a structure that holds data and is uniquely named by the programmer. It holds the data assigned to it until a new value is assigned or the program is finished.

Control Values
Variables are widely used to hold control values that keep track of something. For example, the C statement FOR (X=0; X<5; X++) performs the instructions following the statement within open and closed curly braces ({ and }) five times, and X is keeping track of that number of iterations. X is a variable set to zero (x=0), incremented by 1 (x++) and compared to 5 (x<5). The reason it is less than 5 (<5) is because we started with 0.

The Equals Sign
Variables are usually assigned with an equal sign. Numbers are unquoted; for example: COUNTER = 1 places the digit 1 in the variable COUNTER. Character data (text) requires quotes; for example: PRODUCT = "abc1234". In some languages, the type of data must be declared before it is assigned; for example, in C/C++, the statement INT COUNTER creates a variable that holds only whole numbers (integers).

Local and Global
A local variable is one that is referenced only within the subprogram, function or procedure it was defined in. A global variable can be used by the entire program. See undefined variable and local variable.