Advance-C/C2/Storage-class-specifiers/English-timed

Time	Narration
00:01	Welcome to the spoken tutorial on Storage class specifiers.
00:07	In this tutorial, We will learn about Storage class specifiers auto keyword static keyword extern keyword register keyword with the help of examples.
00:22	For this tutorial I am using Ubuntu Operating system version 11.10 and gcc Compiler version 4.6.1 on Ubuntu
00:34	To follow this tutorial you should be familiar with C tutorials.
00:41	If not, for relevant tutorials please visit our website, which is as shown.
00:47	I will start with an introduction to storage class specifiers.
00:52	* Specifiers tell the compiler where to store a variable.
00:57	How to store the variable.
00:59	What is the initial value of the variable.
01:03	Life time of the variable.
01:06	The Syntax is: storage_specifier data_type variable _name
01:13	Types of storage class specifiers are: auto static extern register
01:21	Let us start with auto keyword.
01:24	Auto keyword declares an automatic variable.
01:28	It has a local scope.
01:30	Keywords are not initialized automatically.
01:34	You should explicitly initialize keywords while declaring
01:39	Storage space of keywords is CPU memory.
01:43	Let us see an example. I have a code file; let us go through it.
01:49	Note that our filename is auto.c
01:54	We have declared a function as “increment”.
01:58	This is the main function.
02:00	In the main function, increment function is called 4 times.
02:06	Then we have the return 0 statment.
02:10	Let us see the function definition
02:14	Here we have declared variable i as auto int. It has a local scope.
02:21	Then we display value of i using printf.
02:26	Value of i is incremented here.
02:30	Let us open the terminal by pressing Ctrl+Alt+T keys simultaneously on your keyboard.
02:38	Type: gcc space auto.c space hyphen o space auto. Press Enter.
02:48	Type dot slash auto
02:51	The output is zero.
02:54	Now come back to our program.
02:57	Let us initialize the auto variable i above the main function.
03:02	I will cut this declaration and initialization from here, and paste it over here. Click on Save
03:14	Let us execute on the terminal. Press the uparrow key twice. Press Enter
03:22	We get an error: file-scope declaration of i specifies auto
03:29	This is because an auto variable is local to the function.
03:34	We cannot initialize it globally.
03:37	Let us fix the error. Come back to our program.
03:42	Delete this; paste it over here.
03:47	Click on Save and execute on the terminal.
03:52	Press the up arrow key. Recall the previous command.
03:57	Press Enter. Type: dot slash auto Press Enter.
04:03	Yes it is working! The output is zero.
04:07	This is because we have initialized the value of i as zero.
04:13	Now let us see static variable.
04:16	Although we have studied about static variable in the previous tutorials. I will explain it here briefly.
04:24	'static' variables are initialized to zero.
04:28	They are not destroyed even after program control exits from the block.
04:35	Value of the variable persists between different function calls.
04:41	Storage space is CPU memory.
04:45	Let us see an example. I will edit the same code file.
04:51	Come back to our program.
04:54	Press Ctrl + Shft + S keys simultaneously.
05:01	Now I will just change the filename as static. Click on Save.
05:10	Now, I will change the initialization of the variable i to static int i equal to zero Click on Save.
05:23	Let us see what happens. Execute the file on the terminal.
05:30	Type: gcc space static.c space hyphen o space stat. Press Enter
05:41	Type dot slash stat . Press Enter
05:46	The output is displayed as: 0, 1, 2, 3
05:51	This is because static variables are global variables.
05:56	The scope of static variable is local to the function they are defined in.
06:03	They do not lose their value between function calls.
06:08	Now let us learn about extern keyword.
06:12	Scope of extern variable is throughout the main program.
06:17	Definition for extern variable might be anywhere in the C program.
06:23	extern variables are initialized to zero, by default.
06:28	They can be accessed by all functions in the program.
06:33	These are stored in CPU memory.
06:36	Let us see an example.
06:38	I have a code file; let us go through it.
06:42	Note that our filename is extern.c
06:47	I have initialized a variable as integer variable x to 10.
06:54	This the main function. In the main function I have declared an extern integer variable y.
07:03	Using the printf statements we will display the values of x and y. This is the return statement.
07:12	We will initalize y to 50 after the main function close.
07:18	Now switch to the terminal and let us see what will be the output.
07:24	Type: gcc space extern.c space hyphen o space ext. Press Enter
07:35	Type: dot slash ext. Press Enter
07:40	The output is displayed as: The value of x is 10 The value of y is 50
07:48	As we studied, the value of the extern keyword is throughtout the main program.
07:55	We can define it anywhere in the program.
07:59	Both the statements are justified.
08:02	Now let us move on to register keyword.
08:06	Register variables will be accessed faster than normal variables.
08:13	They are stored in register memory rather than main memory.
08:19	Limited number of variables can be used since register size is very low.
08:25	16 bits, 32 bits or 64 bits.
08:30	Let us see an example now. I have a code file. Let us go through it.
08:37	Note that the file name is register.c
08:42	Here we have declared register integer variable.
08:47	This variable will be directly stored in the register memory.
08:53	This is the for loop that displays the value of i from 1 to 5.
08:59	This will display the value of i.
09:03	Let us execute the program and see.
09:07	On the terminal, type: gcc space register.c space hyphen o space register
09:17	Press Enter. Type: dot slash register. Press Enter.
09:25	You can see the output is displayed as: Values stored in register memory 1 2 3 4 5
09:34	This brings us to the end of this tutorial. Let us summarize.
09:39	In this tutorial, we learnt- Storage class specifiers auto keyword static keyword extern keyword register keyword
09:52	As an assignment, Write a program to print the sum of first 5 numbers
09:59	Declare both the keywords auto and static in the program
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10:52	This is Ashwini Patil from IIT Bombay. Thank you for joining.

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PoojaMoolya, Pratik kamble, Sandhya.np14