C Function Declaration

In C programming language, a function is a block of code that performs a specific task and can be called from other parts of the program. Functions provide modularity and reusability to programs, and make them easier to read, test, and maintain.

A function in C typically consists of the following parts:

1. Function header: specifies the function name, return type, and parameter list.
2. Function body: contains the statements that define what the function does.
3. Function call: invokes the function from within another part of the program.

The syntax for defining a function in C is as follows:

return_type function_name(parameter1_type parameter1, parameter2_type parameter2, ...) {
    // function body
    return return_value; // optional
}

where:

• return_type: specifies the data type of the value that the function returns (such as int, float, void, etc.).
• function_name: specifies the name of the function (must be a valid identifier in C).
• parameter1_type, parameter2_type, etc.: specify the data types of the parameters that the function expects to receive (such as int, float, char, etc.).
• parameter1, parameter2, etc.: specify the names of the parameters.
• return_value: specifies the value that the function returns (if the return_type is not void).

For example, the following is a definition of a function named sum that takes two integer parameters and returns their sum:

int sum(int a, int b) {
    int result = a + b;
    return result;
}

This defines a function named sum that takes two integer parameters named a and b, adds them together, stores the result in a variable named result, and returns the value of result. To call this function from within another part of the program, we can use the following syntax:

int x = 5;
int y = 7;
int z = sum(x, y); // z will be assigned the value 12