Functions in C

What is a Function in C?

A function is a set of statements that accept inputs, do a specific computation, and return output. The aim is to combine some regularly or repeatedly performed actions into a function so that we may call it instead of writing the same code for different inputs.

Types of Functions in C

Functions in C are classified into two types:

1. Library Functions
2. User-Defined Functions

Library Functions

A "built-in function" is another name for a library function. There is already a compiler package that includes these functions, each with a specific meaning. Built-in functions have the advantage of being directly useable without the need for definition, whereas user-written functions must be declared and defined before they can be used. 

Advantages of Library Functions

• The functions in the C Library are user-friendly and performance-enhancing.
• Function development time is significantly reduced by using C library functions.
• The functions in the C library are reliable and convenient.

User-Defined Functions

User-defined functions or "tailor-made functions" are functions created by the programmer. The programmer can upgrade and modify user-defined functions as needed. When we write a case-specific function that is not defined in a header file, we must declare and define it ourselves using the syntax.

Advantages of User-Defined Functions

• Modifiable functions can be changed to suit your needs.
• The code for these functions is reusable in other programs.
• Debugging, maintaining, and using these functions is simple.

Function Parameters

Information can be used as a parameter in functions. It acts as a variable within the function. Specified within brackets, after the function name. It uses a comma to separate several parameters.

Function Overloading 

If the number and/or type of parameters provided to two functions differ, they can have identical names.​ Overloaded functions are those that share the same name but take different arguments.

Default Argument

A default argument is a value specified in a function declaration that the compiler will assign if the caller function does not give a value for the argument. ​If any value is entered, the default value is overwritten. 

Calling a Function

In C, calling a function consists of invoking its name followed by brackets holding any required parameters. This initiates the function's execution and transfers control to the function body. After completing its purpose, the function may return a value, if declared, that can be assigned or used in the calling context.

Call by Value 

When calling by value, the original value is not changed. The function parameter stores the passed-in value in the stack memory address. Changing the value of a function parameter affects only the current function. This will not alter the value of variables within the caller method, such as main().

Call by Reference

We modify the original value by passing a reference (address). The address of the value is passed in the function, so the actual and formal parameters share the same address space. As a result, any changes to the value within the function are reflected both inside and outside of it.​

Advantages of Functions in C

• The function can reduce the number of repeated statements in the program.
• The method makes our code more readable by adding modularity to it.
• There is no fixed number of calling functions; you can call them as many times as you wish.
• The function decreases the size of the program.
• Once the function is declared, you can just use it without worrying about how it works inside.

Disadvantages of Functions in C

• It is not possible to return multiple values.
• Memory and time overhead occur as a result of stack frame allocation and control transfer.