user-defined-functions-in-c

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In the C programming language, user-defined functions refer to those functions that are crafted and established by the user, facilitating the creation of efficient, organized, modular, and reusable code. In every programming scenario, whether it involves a basic program or extensive software, understanding user-defined functions can simplify your coding process. This article will explore what a user-defined function is, its structure, syntax, invocation methods, parameter passing, advantages, and an illustration of a recursive user-defined function in C.

Table of Contents:

What is a User-Defined Function in C?

A user-defined function in C is a function that a user constructs and specifies for performing a particular programming task. It represents a category of functions in C. This type of function aids users in structuring programs efficiently, in a modular fashion, and allows for reuse. User-defined functions also simplify debugging and can be utilized in various sections of the program. Additionally, they enhance the program’s readability and conserve the user’s effort and time.

Structure of User-Defined Function in C

In C programming, the framework of a user-defined function usually consists of three primary elements:

  1. Function Declaration (Prototype)
  2. Function Definition
  3. Function Call

1. Function Declaration (Prototype) in C

A function declaration represents a prototype in C that informs the compiler regarding the function’s name, parameters, and return type prior to its utilization in the program. This allows the compiler to verify that the function is invoked with the appropriate number and types of arguments. The function declaration is generally placed above the main function within the program.

Syntax:

return_type function_name(parameter_list);

In this context,

  • return_type: This denotes the data type of the value that the function returns.
  • function_name: This is the identifier the user assigns to the function, which must also comply with C naming conventions.
  • parameter_list: This represents the collection of input variables that the function accepts.

Example:

void greet();
int add(int a, int b);

Explanation: The code indicates that the void greet(); declares the greet function, which takes no arguments and returns nothing, while int add(int a, int b); defines an add function that takes two integers as input and returns an integer.

2. Function Definition in C

A function definition in C comprises the actual implementation of the function, the section of code that is executed when it is invoked. A function definition includes a return type, the function name, an optional parameter list, and the instructions within the function’s braces.

Syntax:

return_type function_name(parameter_list) {
// Function body
return value;
}

In this context,

  • return_type: This specifies the type of value that will be returned by the function.
  • function_name: This is the identifier the user is assigning to the function.
  • parameter_list: This is the collection of input variables accepted by the function.
  • Function Body: The code section that executes the necessary operation.
  • Return value: This is the value sent back from the function.

Example:

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

Explanation: The code demonstrates that the add function accepts two integers, a and b, computes their sum, assigns the result to sum, and subsequently returns the sum as an integer.

3. Function Call in C

In C, a function call represents the mechanism through which the user activates a user-defined function. A function call transfers control from the invoking program to the designated function, and during this process, the function may have options for passing parameters and receiving return values, depending on its definition.

Syntax:

function_name(arguments);

In this context,

  • function_name: It is the identifier assigned by the user to invoke the function.
  • arguments: These are the values the user will provide to the function’s parameters.

Example:

int result = add(5, 3);

Explanation: The code illustrates how the add function, with inputs 5 and 3, is used to determine the return value, which is then assigned to the variable result.

Example of a User-Defined Function in C

C

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Output:

Example of a User-Defined Function in C

The code illustrates how a user-defined function, add, is formed, which accepts two integers, 15 and 25, combines them, and returns the total. The add function is invoked in main(), and the sum of 40 is displayed using printf(). This program also demonstrates how the function is declared, defined, and invoked. 

Techniques to Invoke User-Defined Functions in C

Here are the four primary methods that can be utilized to invoke a user-defined function in C.

1. Call by Value

Call by value is the standard method of passing arguments to functions in C programming, where the original values of the variables are transmitted to the function. However, the function receives a duplicate of the variable, so modifications made within the function will not impact the original value. It is a secure and most frequently used technique for basic data types.

Example:

C
Code Copied!

Result:

Call by Value

The snippet illustrates how the modify function adjusts only the replica of the variable a and not its initial value, since the function is delivered by value.

2. Invoking Functions Without Arguments

Invoking functions without arguments is a technique that does not accept any input parameters and carries out the task autonomously. It may or may not yield a value and is employed to display notifications. In this approach, no information is transmitted to a function.

Illustration:

C
Code Copied!

Result:

Calling Functions with No Arguments

The snippet illustrates how the greet function is invoked from the main function, which accepts no parameters and solely prints the message “Hello, welcome to C programming!” upon invocation.

3. Invoking Functions Without a Return Value

Invoking functions without a return value is a technique where the function executes a task but does not provide any value upon call. This function returns nothing, therefore its return type is void. In this approach, the function may or may not receive arguments. It is utilized for displaying output or executing operations that do not require a result.

Illustration:

C
Code Copied!

Output:

Calling Functions with No Return Value

This code illustrates how the displaySum() function is invoked, which accepts two integers, 10 and 20, and logs their sum, 30, to the console, but it does not yield any value back to the caller.

4. Invoking Functions with Parameters and Return Value

Calling functions with parameters and a return value refers to a practice where the function takes input values and subsequently returns a result to the caller. This is the most frequently utilized and versatile type of user-defined function. The function's return type can be anything, such as int, float, char, etc.

Example:

C
Code Copied!
``````html

Result:

Calling Functions with Parameters and Return Value

The code illustrates how the multiply function accepts two integers, 6 and 7, as arguments, computes the product, returns this value to the main function upon invocation, and subsequently stores the product, 42, in the result variable, which is then printed to the console.

Transmitting Parameters to User-Defined Functions in C

Parameters in C can be transmitted to user-defined functions to provide input values by two methods: Pass by Value and Pass by Reference.

1. Pass by Value in C

Pass by value is a technique in which a duplicate of the actual value is forwarded to the function. The function operates on this duplicate, therefore any modifications made within the function do not influence the original variable in the calling function. This is the default approach in C. It is ideal for safeguarding original values, hence the original values remain unaltered.

Illustration:

C
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Result:

Pass by Value in C

The code demonstrates how the modify function alters only the copy of the variable a and not the original value, since the parameters are transmitted by value. Therefore, the value of a remains unchanged outside the function and is printed to the console.

2. Pass by Reference in C

Pass by reference is the approach of passing the address of a variable to a function, allowing the function to directly modify the value of the original variable. In C programming, this is accomplished through the use of pointers. By passing by reference, the function obtains the address of the variable. This method is utilized when multiple values need to be modified within the function.

Illustration:

C

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Output:

Pass by Reference in C

The code illustrates how the modify function utilizes a pointer to directly alter the value of the variable a, as the function receives the address of the variable a. Hence, the modification in the value is also reflected outside the function and subsequently printed to the console.

Variable Scope in User-Defined Functions in C

The extent of the program where a variable in C is accessible is referred to as its scope. Understanding the range of variables within a user-defined function is vital for managing data flow and memory effectively.

1. Local Variables

Local variables are defined within a user-defined function in C and can solely be utilized in that function. These variables are instantiated when the function is called and dismantled when the function concludes.

Example:

C
Code Duplicated!

Result:

Local Variables

The snippet illustrates that the variable x is confined to the show() function and cannot be utilized beyond it; its existence is limited to the function execution period.

2. Global Variables

In C, global variables are defined outside any function, allowing them to be accessed and altered from any function within the same program. The global variable scope encompasses the entire program, which facilitates their use across various functions.

Illustration:

C
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Result:

Global Variables

The snippet demonstrates that the global variable x is available in both main and display functions, thereby allowing shared access to the variable across the functions, which is subsequently printed to the console.

3. Static Variables

Static variables are defined using the static keyword in C, enabling them to retain their value between function invocations. However, they remain local to the function where they were defined.

Illustration:

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Output:

Static Variables

The code illustrates how counters are displayed in the console after the static variable count retains its value across multiple calls to the counter() function.

Recursive User-Defined Functions in C

A user-defined function that invokes itself to accomplish a specific task is referred to as a recursive user-defined function in C. Recursion divides the tasks into smaller, simpler, yet related subtasks. To avert infinite recursion or a stack overflow, a base case is needed for a recursive function. This type of function is frequently used in divide-and-conquer strategies or mathematical problems.

Syntax:

return_type function_name(parameters) {
if (base_condition) {
return result;
} else {
return function_name(modified_parameters); // Recursive call
}
}

Example:

C

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Output:

Recursive User-Defined Functions in C

The code demonstrates how...

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illustrates how the factorial function invokes itself repeatedly until it hits the base condition, where n is equal to 0, and subsequently multiplies the result during the return phase to yield 120.

Advantages of User-Created Functions in C

  • User-created functions break the program into smaller, manageable components, thereby promoting modular code.
  • They assist in organizing the code so that each function is responsible for a specific task.
  • User-created functions can be defined once and invoked multiple times throughout the program.
  • Errors within a user-created function can be easily identified and rectified.
  • User-created functions enhance the program's overall readability.
  • These functions also minimize code repetition within the program.
  • In larger projects, various functions can be crafted and tested independently based on user requirements.

Summary

User-created functions in C are crucial for generating code that is effective, well-organized, and easy to maintain. They simplify complex programs by segmenting them into smaller, reusable, and manageable modules, which aids in understanding and debugging. With the aid of function declarations, definitions, and calls in C programming, creating user-defined functions is straightforward. Hence, grasping user-created functions in C is vital, as they assist with both simple and complex computations or programming tasks.

User-Created Functions in C – FAQs

Q1. What is a user-created function in C?

A user-created function is a function in C that is defined and created by the user to perform a particular programming task.

Q2. Why should I utilize user-created functions?

User-created functions enable you to create code that is more modular (the program can be divided into distinct sections), reusable, easy to read, and simpler to maintain or debug.

Q3. What are the central components of a function in C?

The central components of a user-created function include a declaration (prototype), a definition (body), and a function call.

Q4. What is the standard argument passing method in C?

The standard method is call by value (passing a copy of the variable) for argument passing.

Q5. Can a function return multiple values in C?

Not directly; however, you can return multiple values using pointers or structures.

The article User-Defined Functions in C first appeared on Intellipaat Blog.


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