A function is a block of code that performs a specific task. In C, we can divide a large program into the basic building blocks known as function.
A function can be
called multiple times to provide reusability and modularity to the C program.
Reusability is the main
achievement of C functions. By using functions, we can avoid rewriting same
logic/code again and again in a program.
There are two types of
functions in C programming:
•
Library
Functions: are the functions
which are declared in the C header files such as scanf(), printf(), gets(),
puts(), ceil(), floor() etc.
•
User-defined
functions: are the functions
which are created by the C programmer. It reduces the complexity of a big
program and optimizes the code.
A function will have
three aspects
1. Function Declaration
/ function prototype
2. Function Call
3. Function Definition.
1. Function Declaration / function prototype:
A function must be declared
in a C program to tell the compiler about the function name, function
parameters, and return type.
A function prototype is
simply the declaration of a function that specifies function's name, parameters
and return type. It doesn't contain function body.
Syntax of
function prototype
returnType functionName(type1 argument1, type2
argument2, ...);
Ex:
void sum(int
x, int y);
The function prototype
is not needed if the user-defined function is defined before the main() function.
2. Function
call:
Function can be called
from anywhere in the program. Control of the program is transferred to the
user-defined function by calling it.
Syntax of
function call
functionName(argument1,
argument2, ...);
Ex:
sum(a,b);
3. Function
definition:
Function definition
contains the block of code to perform a specific task. When a function is
called, the control of the program is transferred to the function definition.
And, the compiler starts executing the codes inside the body of a function.
Syntax of function definition
returnType functionName(type1 argument1, type2
argument2, ...)
{
//body of the function
}
Ex:
void sum(int x, int y)
{
int sum=x+y;
printf(“ sum is;%d”.
sum);
}
Different aspects of function calling
There are four
different aspects of function calls:
•
function
without arguments and without return value
Ex: void sum( );
•
function without
arguments and with return value
Ex: int sum( );
•
function
with arguments and without return value
void sum(int a,int b);
•
function
with arguments and with return value
int sum(int a,int b);
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