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What is the Difference Between Variable Declaration and Variable Definition?

Posted in C Programming

In C programming, variable declaration and variable definition are two concepts that are often used interchangeably, but they have different meanings.

Variable declaration is the process of announcing to the compiler the existence of a variable, its type, and name. This is done using the syntax:


DataType VariableName;

For example, int count; declares a variable called count of type int. Variable declaration does not allocate memory for the variable, but it tells the compiler that the variable will be used in the program.

Variable definition, on the other hand, not only declares the variable, but it also reserves memory space for it. This is done by providing an initial value to the variable. The syntax for variable definition is:


DataType VariableName = Value;

For example, int count = 0; declares and defines a variable called count of type int with an initial value of 0. Variable definition implicitly declares a variable, but variable declaration does not define it.

Variable declaration is required before using a variable in a program, while variable definition is optional if the variable is not used. However, if a variable is used without being defined, it will result in a compilation error.

In summary, the difference between variable declaration and definition is that declaration announces the existence of a variable, while definition reserves memory space for it and initializes its value.

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