Definition and declaration

[nishcom]

Would anyone please tell me what is the difference between Declaration and Definition in "c"?

[MaRo]

they're about the look of the function in a program

Definition is writing the function and how it is working like

void foo()
{
printf("foo");
}

Declaration is just writing the function header to implement in another function like:

int main()
{
foo(); // this is declaration
return 0;
}

And of course to write a declaration there should be a definition to implement.

[banu]

Both are based on functions and variables mostly.
EXAMPLE
For declaration
void main()
{
write();
}
write() is a function call which is declared.

For definition:
void write()
{
printf("enter the name");
scanf("%s",name);
}
Here the operation/function of write() is defined.
definition must be given before declaration.
i guess iam right

[Amit Saste]

Originally Posted by nishcom

Would anyone please tell me what is the difference between Declaration and Definition in "c"?

Just giving simple example:

Cnsider following as function declaration:
public void add_ten_nos(int a[]); //This is Declaration

public void add_ten_nos(int a[])
{
int sum;
for(i=0;i<10;i++) //or whatever the Definition
sum=sum+a[i]:
}

Hope u got it!!

[umesh936]

hi
Last one is correct(Amit)

#include<stdio.h>
void display(); // it is declaration
int main()
{
display(); // here it is called
}
// now here is defination of function
void display()
{
printf(" my name is XYZ");
}
///it so simple..

[mohanapriya]

hi i am pri.... actuall dis is my 1st post so i dnt no whether i m posting it to the right place or not.....
i am in desperate need of a topic artificial inteligence on which i want to present a paper.....i feel engineering is absolutely not interesting until u do something technical....so please guide me ...

[Mrunalini]

Hi.. One more additional point is that..

Function Definitions also known as proto-type, they are just an intimation given to the Compiler that I will be using the proto typed function in the future code execution.

The syntax for Prototype is:
<Return type> <Function Name>(Argument Data Types);
Here semicolon is a must, and must be declared before the Function Definition.

Whereas when a function is called the code which is executed is Function Definition, with a syntax:

<Return Type> <Function Name>(arguments and their Datatypes)// No semicolon
{
Body of the code
}


Where as if we consider a variable.
when you declare:
int a;
you are telling the compiler that I am going to use a variable 'a' as an integer variable, please allocate space for it.

So here 'a' stores the address which is allocated by the compiler.
When you say
a = 5;

The value 5 is set to the location 'a' in the memory.

Hope this was helpful..

[kidakaka]

Ill keep the difference simple.

Declaration - you are announcing to the compiler, that such and such function exists. This one shows the existence.
Definition - you are displaying to the compiler, the exact working of such and such function. This one shows the innards and the existence.

[ash]

Ah.. can I use an analogy like this?

Declaration: Mobile phone brand X
Definition: 3G, SMS, mobile gaming, mp3 music, organizer etc etc..

[regalrohit]

hi,in definition,variable space is allocated for variable and for some initial value.

In declaration only intenifies the type of variable for function.In simple word in definition memory space is allocated.
In declartion refer to the place where the variable nature is stated,no allocation is done.
for example

void show()\\"declaration"//
{
printf("singh is king");
}
#include<stdio.h>
void main();\\"definition"
{
void show();
clr scr();
show();
getch();
}