What is a Function in C | Call By Value and Call by Reference In C

Functions in C:

What is a Function?

The function is a block of code to perform a specific task In C. we divide a large program into basic building blocks known as a function. The block contains certain statements of code enclosed by the { }. When a program calls a function, the code inside the function executes and it may return a value back to the calling function.

Advantages of  a Function:

1. By using functions, we can track large programs when it is divided into multiple functions.

2. We can avoid rewriting the code again and again in a program.

3. We can call C functions any number of times from anywhere in the program.

4. We can easily modify the errors that occurred.

5. Code optimization takes place while using the functions.

Function Aspects:

The Aspects of the function are:

1. Function Declaration: A Function must be declared globally in a C program to tell the compiler about the function name, function parameters(formal parameters), and return value.

2. Function Call: The function can be called anywhere from the function. The function parameters list must not differ in function calling and a function declaration.  We must pass the same number of parameters as it is declared in the function declaration.

3. Function definition: It contains the actual statements which are to be executed.

Types of Functions:

There are two types of functions in C:    

    1. Inbuild/Library Functions

    2. User-defined Functions

1. Library Functions: These functions are declared in the C header files such as print(), scanf(), strlen(), pow(), strcpy() etc.

"In this tutorial, we are completely focusing on user-defined functions."

2. user-defined Functions: These functions are created by the Programmer so that these functions are used multiple times. Reusing the code decreases the complexity and increases code optimization.

    Function Declaration without return value: In this declaration, we use void as a return type so that the function cannot return anything.

    Syntax:

    return_type fun_name(parameters_list)

      {

       }

    Example:

   Output:

    Function Declaration with return value: If you want to return any value from the function, you need to use any data type such as int, char, and float. The return type depends on the value to be returned from the function.

     Syntax: 

    return_type  function_name(parameters list)

    {

             // code to execute

             return value;

     } 

    Example: 

   Output:

Function Call: A Function can be called from anywhere and any number of times in a program. The Function call differs in two ways. One is a calling a function and another one is called a function.

While calling a Function there are two methods to pass data into the function in C language.

    1. Call By Value

    2. Call By Reference

    Call By Value: 

• The actual parameter is the argument that is used in the function call whereas the formal parameter is the argument that is used in the function definition.    

• Different Memory locations are allocated for actual and formal parameters.

• In call by value method, the value of actual parameters is copied into the formal parameters.

• In call by value method, we can not modify the value of the actual parameter by the formal parameter.

     Example: Consider the following example for the call by value in C.

    program:

  

     Output:

  

     Explanation: When the function sample is called, the value of x  is passed as an argument to the called function. To store the value passed by the calling function, you need to declare the formal parameter as a variable. According to call by value, the value of the actual parameter(x) remains the same even the formal parameter(y) gets changed. 

    Call By Reference:

• In call By Reference, the memory location is similar for both actual and formal parameters.
• All the operations in the function are performed on the value stored at the address of actual parameters. The modified value get stored at the same address. 
• In Call By Reference, the address of actual parameters is passed into the formal parameters.
• The value of actual parameters can be modified by changing the formal parameters since the address of actual parameters is passed.    

     

     Example: Consider the following example for the call by reference in C.

    program:

  

     Output:

 

   Explanation: When the function sample is called, the address of x is passed as an argument to the called function. To store the address passed by the calling function, you need to declare the formal parameter as a pointer(*y). According to call by reference, the value of the actual parameter(x) gets modified by changing the formal parameter(y). 

Example: Program for passing an array to a function.

    Program:

   Output:

 

    

    In this tutorial, we have learned about the C function, how to define your own functions and how to pass arguments to a function in a different way.

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