Function Declaration & Definition In C Language

In the C programming language, a function must be declared before it can be called in a program. A function declaration, also known as a function prototype, tells the compiler the name of the function, the types of its parameters, and the type of value it returns. A function definition, on the other hand, provides the actual code for the function.

Function Declaration: The syntax for declaring a function in C is as follows:

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return_type function_name(parameter1_type parameter1, parameter2_type parameter2, ...);

For example, a function named "add" that takes two integer arguments and returns an integer might be declared as follows:

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int add(int a, int b);

Function Definition: The syntax for defining a function in C is similar to the syntax for declaring a function, with the addition of the function body. The function body is a block of code enclosed in curly braces {}.

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return_type function_name(parameter1_type parameter1, parameter2_type parameter2, ...) {    // function body }

For example, a function named "add" that takes two integer arguments and returns their sum might be defined as follows:

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int add(int a, int b) {    return a + b; }

It is important to note that the function declaration and definition should match exactly, including the name, return type, and parameter types.

Once a function is defined, it can be called by using its name and passing the required arguments.

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int result = add(2, 3); //result = 5

It is also possible to have a function definition without a matching declaration, but this is not recommended practice, especially when the function is called in multiple places in the code, as the compiler will not know the return type and parameter types of the function.