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 Data Types & Variables
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.
	What is a token? Token is a generic word for Data types, Variables, Constants and Identifiers
Slide 3	To record this tutorial, I am using Ubuntu Operating system version 11.10 gcc and g++ Compiler version 4.6.1 on Ubuntu
Let us switch to the file variable.c	Let us start with the program I have already typed the program on the editor So i will open it
	Let me explain the code now
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.
	Now, let us swtich back to our slides. The syntax for initilization is, datatype varname = value;
	Datatype defines the type of the variable. varname is the name of the variable. We can assign it a value here.
Slide 4	Keywords have fixed meanings that cannot be changed Keywords cannot be used as variable names There are 32 keywords available in C To name some, auto, break, case, char, const, default, enum extern, etc.
	Come back to our program.
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
Highlight float c	Here, float is a data type of c
Highlight float c = 1.5;	We have assigned it a value, 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 Let us now switch back to the slides and know more about constants, datatypes and variables
Slide 5	Let us switch to the slides to know more about constants Constants are fixed values They do not change during the execution of a program There are two types of constants Numeric constants Character constants
Slide 6	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 use char and %c For double data type, we use double and %lf.
Slide 7	Now we will see the range of data types (We CANNOT store a value in the variable above or below the range of its data type) The value stored in the variable must not be greater or less than the range Integer value has a range of -32,768 to 32,767 Floating point has a range of 3.4E +/-38 Character has a range of -128 to 127 Double has a range of 1.7E +/-308
Slide 8	Variable is a data name It may be used to store a data value The values can change when a program runs It must be declared before using a variable We should try to give meaningful names to variables example john, marks, sum etc.
On the editor	Now come back to our program.
Highlight printf("The Value of a is %d\n", a);	Here, printf is the identifier name for this function These cannot be used as keywords.
	Let us go back to our slides to know more about our identifiers.
Slide 9	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.
	Come back to our program Click on Save to save the program
Ctrl, Alt and T keys simultaneously	Let us execute the program Let us open the terminal by pressing Ctrl, Alt and T keys simultaneously.
	To compile the program
Type gcc variable.c -o var	Type gcc tokens.c -o tok and press Enter
Type ./var	To execute this file, let us type ./tok
	The output is displayed. We can see that here we have six values after the decimal point. And here we have only two values after the decimal point.
	Now let us find out how this happened.
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 I want an output with three decimal places.
	Let us replace %.2f with %.3f
	Click on Save Come back to the terminal
On the terminal	Now let us compile using the same command we used before execute the program Come back to the terminal
Highlight 1.500	We see the output as 1.500 We can see here three values after the decimal point. Let us go back to the program.
	NOW LET US SEE HOW TO EXECUTE THE SAME PROGRAM IN C++ Come back to our program
	Let me change a few things here
Type <iostream>	First we will change the header file <iostream>
Type using namespace std;	We will include the using statement here
Type cout<<	Now replace the printf statement with cout statement Since we use cout<< function to print a line in C++
%d	We don't need the format specifier here So let us delete it
	Now type two opening angle brackets here <<a let us type \n here so again type two opening brackets Within the double quotes type \n Now delete this bracket. Same way here also.
	Now go to File click on Save as Save the file with .cpp extension
	Let us compile Come back to the terminal
	Type g++ variable.cpp -o var press Enter To execute Type ./var
	Here the output is displayed
Errors Type %d	Now we will see the common errors which we can come across Suppose here we type the %d in the place of %f I will retain rest of the code as it is
Click on save	save the program
On the terminal	Let us go to the terminal Let us compile the program
Highlight format specifier ‘%d’ expects type ‘int’, but argument 2 has type ‘double’	we see a warning format specifier ‘%d’ expects type ‘int’, but argument 2 has type ‘double’
Error 2 Highlight a	Let us see another common error which we can come across. Here we have declared a as integer
Type 8	I will assign a new value to a.
Click on save	save the program.
On the terminal	let us compile it Switch to the terminal
Highlight a = 8;	We see that the output is displayed as the value of a is 8. The new value is printed.
On the editor	Let us switch back to the program
b = 9;	Now suppose here i will change the value of b
Click on save	click on save switch back to the terminal
On the terminal	Let us compile
Highlight error	We see that there is an error As b is an integer constant variable It is a read only variable We cannot change the value of b.
	Let us go back to our program
Delete ' '	Suppose here we forget the single quotes, let us see what happens
On the terminal	Switch to the terminal Let us compile and run
Highlight Z is undeclared	we see an error that Z is undeclared As anything within single quotes is considered as a character value
Slide 10 Assignment	As an assignment Write a C program to calculate the simple interest. Hint: Simple Interest = principal * rate * time / 100
Slide 11 About the Spoken Tutorial Project	Watch the video available at 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 12 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, contact us at the following id contact@spoken-tutorial.org
Slide 13 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: http://spoken-tutorial.org\NMEICT-Intro
	Ashwini Patil from IIT Bombay Thank You for joining

Contributors and Content Editors

Ashwini, PoojaMoolya