Difference between declaration,assignment & initialization

There is few things in C sound like the same but all are carrying different meaning.
I found many people who have got good programming knowledge of C (i don't... Haha).
But still they are not clear with very basic terminology and believe me, for clearing the interview this is the imp thing that interviewer looks into you .

Sometime what happens .....we know what we have been asked for ....but we start answering something else because we know that thing by some different name(terminology)...

You should be very much clear with the standard terminology that you are going to use in Interview.....

Once one of my friend has gone to interview as fresher in Quinnox Bangalore. He answered some questions well but the moment interviewer asked

Can you please explain the difference between Initialization,Assignment and Declaration???

He was like bla bla bla .....

So it happens in many cases, specially if you are fresher Be ready for such kind of question.....

Anyway we are discussing here:

Initialization , assignment , declaration

******************************************************
declaration means creating a variable, each variable that are used in program must declare.

Let's assume we are creating one variable.

                int a;

so this comes under variable declaration......
we can say we are creating a new variable....
creating variable is local word don't use in interview.
we are just declaring it so that we can use it in further part of programming...
once we declare the variable we can't declare the same variable again otherwise compiler will get ambiguity..

later if we need to put some value inside this variable....
So we go like this...
 

 

              a=10;

This is purely assignment....and assignment can be done n no. of times in a program.there is no such restriction on it.

Assignment: throwing away the old value of a variable and replacing it with a new one.It can be done anywhere in the whole program....

"=" is known as assignment operator(right to left).

In this example earlier "a" was holding garbage value.now we replaced it with 10.

 

Initialization: Declaring a variable and assigning a value at the declaration time only is called initializing a variable

eg:

       

        int a=10;      //initializing variable....

      

Initialization = declaration + assignment    at single step.....

Hope that Diagram makes you more clear about these 3 term.


In later post we'll discuss about
Function calling
Function Definition
and Function declaration


and of course how many ways to read ( int *p;) in front of interviewer.

Variable in C

Variable in C

First thing in any programming language is Variable because in any program of any language
we must require variable for keeping the data and proceeding it further so let's understand What variable is...


A variable is named location of data having one address provided by compiler. In other word we can say variable is container (storage area) of data.

What is Data ?

Any thing which we can store ,can be taken as data like (any number,any character, any string ,any file/img etc.)
 

In real world we have used various type containers for specific purpose. For example we have used suitcase to store
clothes, match box to store match sticks etc. In the same way variables are used to store
data.

For example integer variables are used to store integer kind of value ,char variables is used to store characters etc. On the basis of how many data a variable will store, we can categorize the all C variable in three groups.

(a)Variables which can store only one data at time. Example: integer variables, char variables, pointer variables etc.

(b)Variables which can store more than one data of similar type at a time. Example: array variables

(c) Variables, which can store more than one value of dissimilar type at a time. Example: structure or union variables.

Properties of variable in c:

Every variable in C have three most fundamental attributes. They are:

1. Name

2. Value

3. Address

Name of a variable:

 Every variable in C has its own name. A variable without any name is not possible in C.
 Most important properties of variables name are its unique names.
Not two variables in C can have same name with same visibility.
if at all we dare to have the same name of two variable compiler will confuse while processing its data
so it will throw compile time error.
 

For example:

#include<stdio.h>
int main()
{
    auto int a=5;   //Visibility is within main block
    static int a=10; //Visibility is within main block

/* Two variables of same name */
    printf("%d",a);
    return 0;
}


Output: compilation error



But it is possible that two variable with same name but different visibility. In this case variable name can access only that variable which is more local. In C there is not any way to access global variable if any local variable is present of same name. For example:

(a)

#include<stdio.h>
int a=50; //Visibility is whole the program

int main()
{
    int a=10; //Visibility within main block
    printf("%d",a);
    return 0;
}

Output: 10


(b)

#include<stdio.h>

int main()
{
    int a=10; //Visibility within main block.
    {
        a+=5; //Accessing outer local variable a.
        int a=20; //Visibility within inner block.
        a+=10; //Accessing inner local variable a.   
        printf(“%d”,a);//Accessing inner local variable a.
    }

    printf(“%d”,a); //Accessing outer local variable a.
    return 0;
}

Output: 30 15

Address of the variable we need not to worry about that because it automatically allots by the compiler
we can not predict it...although we can also play with addresses once we enter into pointer concept(Back Bone) of C Laungauge...

Welcome everyone in this blog ..This blog is basically for those who are keen to learn C laungauge in easy steps by sachin sir.

About Sachin Sir:

He is the well known faculty in bhopal for his great contribution towards teaching C C++ and other courses.
His way of teaching is absolutely perfect there is no doubt in it..He actually understands in what way student can get the point and exactly in that way he starts teaching the subject.This is something for which every student looks to it .

Every Engineering student in Bhopal believes that it is just like a wasting time if you haven't learn C C++ by sachin sir after spending 4yr of you engg.