C-and-C++/C2/Tokens/English-timed

Time	Narration
00:01	Welcome to the spoken tutorial on Tokens in C and C Plus Plus.
00:06	In this tutorial we will learn ,
00:09	How to define and use tokens.
00:12	We will do this with the help of an example.
00:15	We will also see some common errors and their solutions.
00:20	To record this tutorial, I am using Ubuntu Operating system version 11.10,
00:26	gcc and g++ Compiler version 4.6.1.
00:33	Let us start with an introduction.
00:36	Token is a generic word for data types, variables, constants and identifiers.
00:46	Let us start with our program.
00:49	I have already typed the code on the editor.
00:53	Let me open it.
00:56	Note that our file name is 'tokens.c'.
01:04	In this program we will initialize the variables and print their values.
01:09	Let me explain the code now.
01:12	This is our header file.
01:16	This is our main function.
01:20	Here, int is a keyword.
01:22	The compiler knows the meaning of keyword.
01:26	a is an integer variable.
01:28	We have assigned a value of 2 to it.
01:32	This is called as initialization.
01:35	If a value is not assigned to a variable then it is called as declaration of the variable.
01:43	Here, b is a constant.
01:46	We have initialized 'b' by assigning a value of 4 to it.
01:53	const keyword is used to create 'read only' variable.
01:58	Let us switch back to our slides to know more about keywords and constant.
02:06	Keywords have fixed meanings that cannot be changed.
02:11	Keywords cannot be used as variable names.
02:15	There are 32 keywords in C.
02:18	To name some, auto, break, case, char, enum, extern, etc.
02:28	Constants: constants are fixed values.
02:33	They do not change during the execution of a program.
02:38	There are two types of constants, Numeric constants and Character constants.
02:45	Now come back to our program.
02:47	Here, float is a data type of variable c.
02:52	We have assigned it a value of 1.5.
02:56	Data type is a finite set of values along with a set of rules.
03:04	Here, d is a variable.
03:07	char and single quotes suggest that we are dealing with a character.
03:12	As a result, d is a character variable storing the value A.
03:20	It is easy to see that int, double, float and char are data types.
03:30	a, c and d are variables.
03:35	Now come back to our slides.
03:37	We will know more about data types and variables.
03:48	Data types: Let us begin with integer data type.
03:50	It is declared as int.
03:53	If we want to print an integer data type , we will use %d as the format specifier.
04:01	Similarly, we will use float and %f for floating point numbers.
04:09	For character data type, we will use char and %c.
04:15	And For double data type, we will use double and %lf as the format specifier.
04:24	Now we will see the range of data types.
04:29	Integer data type has a range of this
04:34	Floating point has a range of this
04:39	Character has a range of this
04:42	And Double has a range of this
04:47	The values stored in the variable must not be greater or less than this range.
04:56	Now we will move on to variables.
05:00	Variable is a data name.
05:02	It may be used to store a data value .
05:06	The values can change when a program runs.
05:10	Before using a variable it must be declared.
05:14	We should try to give meaningful names to variables.
05:18	example john, marks, sum etc.
05:24	Now we will move back to our program.
05:27	Here, printf is the identifier name for this function.
05:32	Come back to our slides.
05:35	Let us know about identifiers.
05:38	Identifiers are user defined names.
05:41	An identifier consists of letters and digits.
05:46	Both uppercase and lowercase letters are permitted.
05:51	First character must be an alphabet or underscore.
05:55	Now Come back to our program.
05:58	Here we have initialized the variables and constants.
06:02	Here we print them.
06:05	And this is our return statement.
06:08	Now click on Save.
06:10	Let us execute the program.
06:12	Please open the terminal window by pressing Ctrl, Alt and T keys simultaneously on your keyboard.
06:21	To compile, type gcc space tokens dot c space hyphen o tok. Press Enter.
06:30	To execute, type ./tok (dot slash tok).
06:35	The output is displayed.
06:39	We can see that here we have six values after the decimal point.
06:44	And here we have two values.
06:48	Now let us find out how this happened. Come back to our program.
06:54	This is because we have % point 2f here.
06:59	It denotes that we can print only two values after the decimal point.
07:04	Suppose here I want an output with three decimal places.
07:09	Let us replace % point 2f with % point 3f.
07:16	Now click on Save.
07:19	Come back to our terminal.
07:22	Compile as before, execute as before.
07:28	We see here three values after the decimal point.
07:33	Now we will execute the same program in c++.
07:36	Come back to our program.
07:40	I will change a few things here.
07:42	First press Shift+Ctrl+s keys simultaneously on your keyboard.
07:50	Now save the file with an extension .cpp and click on Save.
07:58	Let us change the header file as iostream
08:03	Now include the using statement.
08:08	And click on Save.
08:11	Now replace the printf statement with the cout statement
08:15	since we use cout<< function to print a line in C++.
08:21	Click on Search for and replace text option.
08:27	Type here printf opening bracket “(”
08:33	And here in this column type, cout and two opening angle brackets “<<”.
08:40	Now click on Replace All and click on Close.
08:45	We don't need the format specifier and '\n'
08:50	Let us delete them.
08:52	Now delete the comma and type two opening angle brackets.
09:01	Click on Save. Now delete the closing bracket.
09:04	Type two opening angle brackets again.
09:09	And within the double quotes type \n.
09:16	Now Click on Save.
09:20	Let us execute the program. Come back to our terminal.
09:24	To compile, type g++ space tokens dot cpp space hyphen o space tok1.
09:35	Here we have tok1 because we don't want to overwrite the output parameter tok for the file tokens.c.
09:46	Now press Enter.
09:48	To execute, type ./tok1 . Press Enter.
09:55	The output is displayed.
09:59	Now let us move on to some common errors which we can come across.
10:03	Come back to our program.
10:05	Suppose here I will reassign a new value to b as 8.
10:12	Now click on Save. Let us see what happens.
10:15	Come back to our terminal.
10:17	Let me clear the prompt.
10:22	Now compile as before.
10:26	We see an error at line no.7 in our tokens. cpp file.
10:32	"Assignment of read only variable 'b' ".
10:36	Come back to our program.
10:39	This is because 'b' is a constant. Constants are fixed values.
10:45	They do not change during the execution of program.
10:49	Hence it is giving an error. Let us fix the error.
10:54	Delete this. Click on Save.
10:57	Let us execute again. Come back to our terminal.
11:01	Compile as before.
11:03	Execute as before. Yes, it is working.
11:09	Now we will see another common error.
11:12	Switch back to our program.
11:15	Suppose here I will miss the single quotes. Click on Save.
11:21	Let us execute. Come back to our terminal.
11:25	Compile as before.
11:28	We see an error at line no.9 in our tokens dot cpp file.
11:34	" 'A' was not declared in the scope". Come back to our program.
11:40	This is because anything within the single quotes is considered as a character value.
11:47	And here we have declared 'd' as a character variable.
11:53	Let us fix the error. Type single quotes at line no.9 here.
11:59	Now Click on Save. Let us execute.
12:02	Come back to our terminal.
12:04	Now Compile as before.
12:06	Execute as before. Yes it is working.
12:13	Now switch back to our slides.
12:15	Let us summarize.In this tutorial we learnt,
12:18	Data types eg. int, double, float etc.
12:24	Variables eg. int a=2;
12:29	Identifiers eg. printf() and
12:34	Constant eg. double const b=4;
12:40	As an assignment,Write a program to calculate the simple interest.
12:45	Hint: principal * rate * time upon 100.
12:50	Watch the video available at the link shown below.
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12:56	If you do not have good bandwidth, you can download and watch it.
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13:35	Ashwini Patil from IIT Bombay signing off .Thank You for joining.

Contributors and Content Editors

Jyotisolanki, Krupali, PoojaMoolya, Pratik kamble, Sandhya.np14, Sneha