What is the Difference Between Declaration and Definition in C?

The main difference between declaration and definition in C lies in the information provided and the memory allocation.

• Declaration: A declaration provides basic information about a variable, function, or class, such as its name and type. It does not allocate memory for the variable or function. For example, when declaring a function without providing its body, the compiler is informed about the existence of the function and its parameters but does not allocate storage for it.
• Definition: A definition, on the other hand, provides all the necessary details about a variable, function, or class, including its type, name, and value or function body. Memory is allocated during the definition process. For instance, when defining a function with its body, the system allocates memory for the function and associates an identifier with it.

In summary:

A variable or function can be declared multiple times, but it can be defined only once.

Comparative Table: Declaration vs Definition in C

The difference between declaration and definition in C is as follows:

In C, a declaration merely provides information that a function or variable exists and gives its type, while a definition allocates memory for the variable or function and provides all the necessary details.