Declaration and
Definition of a Function
Declaration and
definition are two different things. Declaration is the prototype of the
function, that includes the return type, name and argument list to the function
and definition is the actual function code. Declaration of a function is also
known as signature of a function. As we declare a variable like int x; before
using it in our program, similarly we need to declare function before using it.
Declaration and definition of a function can be combined together if we write
the complete function before the calling function. Then we don’t need to
declare it explicitly. If we have written all of our functions in a different
file and we call these functions from mani()
which is written in a defferent file. In this case, the main(
) will not be compiled unless it knows about the functions declaration.
There we write the declaration of functions before the main() function. Function declaration is a one line
statement in which we write the return type, name of the function and the data
type of arguments. Name of the arguments is not necessary. The definition of
the function contains the complete code of the function. It starts with the declaration
statement with the addition that in definition, we do write the names of the
arguments. After this, we write an opening brace and then all the statements,
followed by a closing brace.
If the
function square is defined in a separate file or after the calling function,
then we need to declare it:
Delaration:
Double
square (double);
Definition:
Double square (double number)
{
return
(my_num * my_num);
}
Here
is the complete code to elaborate the topic more:
#include
<iostream.h>
//Here we are
declaring the function.
double
square(double);
main(){
double num, result;
result = 0;
num = 0;
cout<<”Please Enter a Number
to calculate the square of.”;
cin>>num;
//now we are going to call the
function
result = square (num);
cout <<”The square of
”<<num<<”is”<<result;
// function to calculate the square of a
number
double square ( double num)
{
return (num *
num ) ;
}
}
A function in a
calling program can take place as a stand-alone statement, on hand side of a statement. This can be a part of an assignment
expression.
