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

Title of script: Tokens in C

Author: Ashwini R. Patil

Keywords: Tokens, Data types, Variables, Identifiers, Constant, Video Tutorial

Visual Cue	Narration
Slide 1	Welcome to the spoken tutorial on Tokens in C and C++.
Slide 2	In this tutorial we will learn how, To define and use tokens. We will do this with the help of an example. We will also see some common errors and their solutions.
Slide 3	To record this tutorial, I am using Ubuntu Operating system version 11.10. gcc and g++ Compiler version 4.6.1
Slide 4	Let us start with an introduction. Token is a generic word for Data types, Variables, Constants and Identifiers.
Let us switch to the file variable.c	Let us start with the program I have already typed the code on the editor Let me open it
Point the cursor on tokens.c	Note that our filename is tokens.c
	In this program we will initialize the variables and print their values.
	Let me explain the code now
#include<stdio.h> int main()	This is our header file. This is our main function.
Highlight int a = 2;	Here, int is a keyword The compiler knows the meaning of keywords.
Highlight int a	a is an integer variable
Highlight int a = 2;	We have assigned a value of 2 to it. This is called as initialization.
	If a value is not assigned to a variable then it is called as declaration of the variable.
Highlight double const b = 4	Here, b is a constant. We have initialized b, by assigning a value of 4 to it.
Highlight double const b = 4;	const keyword is used to create read only variable
	Let us switch back to our slides to know more about keywords and constant
Slide 5	Keywords have fixed meanings that cannot be changed Keywords cannot be used as variable names There are 32 keywords in C To name some, auto, break, case, char, enum extern, etc.
Slide 6	Constants Constants are fixed values. They do not change during the execution of a program. There are two types of constants. Numeric constants. and Character constants.
	Now Come back to our program.
Highlight float c	Here, float is a data type of variable c.
Highlight float c = 1.5;	We have assigned it a value,of 1.5. Data type is a finite set of values along with a set of rules.
Highlight char d = 'A';	Here, d is a variable Char and single quotes suggest that we are dealing with a character As a result, d is a character variable storing the value 'A'
Highlight a and c	It is easy to see that int, double, float and char are datatypes. a, c and d are variables. Now come back to our slides. We will know more about datatypes and variables.
Slide 7	Datatypes Let us begin with integer data type It is declared as int If we want to print an integer, we will use %d as the format specifier Similarly, we will use float and %f for floating point numbers For character data type, we will use char and %c And for double data type, we will use double and %lf as the format specifier.
Slide 8	Now we will see the range of data types Integer datatype value has a range of this. Floating point has a range of this. Character has a range of this. And Double has a range of this. The values stored in the variable must not be greater or less than this range. Now we will move on to variables.
Slide 9	Variable is a data name. It may be used to store a data value . The values can change when a program runs. Before using a variable it must be declared. We should try to give meaningful names to variables example john, marks, sum etc.
On the editor	Now we will move back to our program.
Highlight printf("The Value of a is %d\n", a);	Here, printf is the identifier name for this function
On the slides	Come back to our slides. Let us know about identifiers.
Slide 10	Identifiers are user defined names An identifier consists of letters and digits Both uppercase and lowercase letters are permitted First character must be an alphabet or underscore.
On the editor	Now come back to our program.
	Here we have initialized the variables and constants. Here we print them.
	And this is our return statement. Now click on Save
Ctrl, Alt and T keys simultaneously	Let us execute the program. Please open the terminal window by pressing Ctrl, Alt and T keys simultaneously on your keyboard.
Type gcc tokens.c -o tok	To compile type, gcc space tokens.c space -o space tok press Enter
Type ./var	To execute type, ./tok
Highlight Output	The output is displayed. We can see that here we have six values after the decimal point. And here we have two values.
	Now let us find out how this happened. Come back to our program.
Highlight printf("The Value of c is %.2f", c);	This is because we have %.2f here. It denotes that we can print only two values after the decimal point.
Type	Suppose here I want an output with three decimal places.
Replace %.2f with %.3f	Let us replace %.2f with %.3f
Click on Save	Now click on Save Come back to the terminal
On the terminal	Compile as before execute as before
Highlight 1.500	We see here three values after the decimal point.
	NOW WE WILL EXECUTE THE SAME PROGRAM IN C++ Come back to our program.
	I will change a few things here.
	First press shift+ctrl and s keys simultaneously on your keyboard.
	Now save the file with an extension .cpp and click on save.
Type <iostream>	Let us change the header file as <iostream>
Type using namespace std;	Now include the using statement And click on Save.
Type cout<<	Now replace the printf statement with cout statement Since we use cout<< function to print a line in C++
Click on Search for and replace text option printf( cout <<	Click on Search for and replace text option Type here printf opening bracket “(” And here in this column type, cout and two opening angle brackets “<<”.
click on Replace All option and Close.	Now click on Replace All and click on Close.
%d	We don't need the format specifier and \n Let us delete them.
	Now delete the comma and Type two opening angle brackets.
Click on Save delete ( Type << “\n”	Click on Save Now delete the closing brackets. Type two opening angle brackets again. And within the double quotes type \n Now Click on Save
On the terminal	Let us execute the program. Come back to the terminal.
Type gcc tokens.c -o tok1 Type ./tok1	Type To compile type: g++ space tokens.c space -o space tok1 Here we have tok1 Because we don't want to overwrite the output parameter tok for the file tokens.c Now press Enter
	To execute Type ./tok1 press Enter
Highlight Output	The output is displayed.
Errors Type %d	Now let us move on to the common errors which we can come across. Come back to our program. Suppose here I will reassign a new value to b as 8.
Click on save	Now Click on Save. Let us see what happens.
On the terminal	Come back to our terminal. Let me clear the prompt. Now compile as before.
Highlight error	We see an error at line no.7 in our tokens.cpp file. Assignment of read only variable b. Come back to our program This is because b is a constant. Constants are fixed values. They do not change during the execution of program. Hence it is giving an error.
Click on Save	Let us fix the error. Delete this. Click on Save Let us execute again Come back to our terminal
Compile and Execute	Compile as before. Execute as before. Yes it is working.
	Now we will see another common error. Switch back to our program.
	Suppose here I will miss the single quotes. Click on Save let us execute.
On the terminal	Come back to our terminal. Compile as before.
Highlight	we see an error at line no.9 in our tokens.cpp file. A was not declared in the scope. Come back to our program. This is because anything within the single quotes is considered as a character value. And here we have declared d as a character variable.
	Let us fix the error. Type single quotes at line no.9 here.
	Now click on Save Let us execute. Come back to our terminal Now Compile as before Execute as before. Yes it is working. Now switch back to our slides.
	Let us summarize In this tutorial we learnt, Data types eg. int, double, float etc. Variables eg. int a=2; Identifiers eg. printf() Constatnt eg. double const b=4;
Slide 11 Assignment	As an assignment Write a C program to calculate the simple interest. Hint: Simple Interest = principal * rate * time / 100
Slide 12 About the Spoken Tutorial Project	Watch the video available at the link shown below http://spoken-tutorial.org /What\_is\_a\_Spoken\_Tutorial It summarises the Spoken Tutorial project If you do not have good bandwidth, you can download and watch it.
Slide 13 Spoken Tutorial Workshops	The Spoken Tutorial Project Team Conducts workshops using spoken tutorials Gives certificates to those who pass an online test For more details, Please write to contact@spoken-tutorial.org
Slide 14 Acknowledgement	Spoken Tutorial Project is a part of the Talk to a Teacher project It is supported by the National Mission on Education through ICT, MHRD, Government of India More information on this Mission is available at the link shown below: http://spoken-tutorial.org\NMEICT-Intro
	Ashwini Patil from IIT Bombay Thank You for joining

Contributors and Content Editors

Ashwini, PoojaMoolya