C-and-C++/C2/Logical-Operators/English

Title of script: Logical Operators in C and C++

Author:Ritwik Joshi

Keywords: Logical Operators, Video Tutorial

Visual Cue	Narration
Slide 1	Welcome to the spoken tutorial on Logical operators in C and C++.
Slide 2	In this tutorial we will learn about: Logical Operators like Logical AND Eg- expression1 && expression2 Logical OR Eg- expression1 || expression2 Logical NOT Eg- !(expression1) We will do these with the help of examples.
Slide 3	To record this tutorial, I am using: Ubuntu 11.10 as the operating system gcc and g++ Compiler version 4.6.1 on Ubuntu.
Slide 4 Non zero = True Zero = False	Let us start with the introduction to the logical operators. In C and C++, true is any value, other than 0. Non-zero means true. Zero means false Expressions using logical operators return 1 for true and 0 for false.
	Now I'll explain the logical operators with the help of an example.
Switch to logical.c in gedit	Here is the program for logical operators in C.
Highlight int a,b,c;	Inside the main block, this statement declares the variables a,b and c as integers.
Highlight printf("Enter the values of a,b and c \n");	The printf statement prompts the user to enter the values of a,b and c.
Highlight scanf("%d %d %d", &a, &b, &c);	The scanf statement takes input from the user for the variables a, b and c.
Highlight if((a > b) && (a > c)) printf("a is greatest \n");	Here, we are comparing the values of a with b and c to find the greatest. To compare simultaneously, we use the logical AND operator. Here, all of the conditions have to be true for logical AND to return a true value. The expression is not evaluated further on encountering a false condition. So, the expression (a>c) is evaluated only if (a>b) is true. If a is less than b, then the expression won't be evaluated further. This statement is be evaluated if the previous condition is true.
Highlight else if (b > c)	Next (b>c) is evaluated.
Highlight printf("b is greatest \n");	If the condition is true, then b is greatest is displayed on the screen.
Highlight else printf("c is greatest \n");	Otherwise c is greatest is displayed on the screen.
Highlight if(a == 0 || b == 0 || c == 0)	We now come to the logical OR operator. Here, any one of the conditions has to be true for logical OR to return a true value. The expression is not evaluated further on encountering a true condition. So, if a == zero, then the remaining two expressions won't be evaluated.
Highlight printf("The product of a, b and c is zero \n");	This printf statement is executed, if, either of a, b or c is 0.
Highlight return 0; }	Coming to the end of the program. return 0 and ending curly bracket.
Click on Save	Now save the program. Save it with extension .c I have saved my file as logical.c
press Ctrl, Alt and T keys simultaneously.	Open the terminal by pressing Ctrl, Alt and T keys simulataneously.
Type gcc space logical.c space -o space log Press Enter Type ./log Press Enter	To compile the code, type gcc space logical.c space -o space log Press Enter. To execute, type ./log Press Enter.
Output:	I will enter the values as 0 34 and 567. The output is displayed as here, c is greatest. And The product of a, b and c is zero. You should try executing this program with different sets of inputs.
	Now, let's write the same program in C++
Open the C++ file.	I have already made the program and will take you through it. Here is the code in C++.
//Logical operators in C++ #include <iostream> using namespace std; int main() { int a,b,c; cout <<"Enter the values of a,b and c \n"; cin >>a >>b >>c; if((a > b) && (a > c)) cout <<"a is greatest \n"; else if (b > c) cout <<"b is greatest \n"; else cout <<"c is greatest \n"; if(a == 0 || b == 0 || c == 0) cout <<"The product of a, b and c is zero \n"; return 0; }	Now to make the same program in C++, we make a few changes. There's a change in the header file. The using statement has been used. Also there is a difference in output and input statements. The operators behave in the same way as they did in C.
Click on Save. point to .cpp	Click on Save. Make sure the file is saved with extension .cpp
press Ctrl, Alt and T keys simultaneously.	Open the terminal by pressing Ctrl, Alt and T keys simulataneously.
On the terminal type g++ logical.cpp -o log to execute ./log	To compile the program, type g++ logical.cpp space -o space log1 Press Enter. To execute, type ./log1 Press Enter.
Output:	I will enter the values as 0 34 and 567. So we see the output is similar to the C program. You should try executing this program with different sets of inputs too.
Errors	Now let us see an error which we can come across. Let us switch back to the editor.
Delete if(a > b) && (a > c)	Suppose here we forgot the brackets. Delete this and this.
	Let us see what will happen. Save the program. Come back to the terminal. Compile and execute as before.
Highlight Error	We see the error: Expected identifier before '(' token.
	This is because we have two different expressions here. We have to evaluate them as one expression using AND operator.
	Now let us go back to our program and fix the error.
	Let us insert the brackets here and here. Click on Save. Come back to the terminal.
	Compile and execute as before. So, it is working now. Let us now summarize the tutorial.
Summary:	In this tutorial we learnt about && Logical AND eg. ((a > b) && (a > c)) || Logical OR eg. (a == 0 || b == 0 || c == 0)
Assignment:	Assignment Write a program that takes two numbers as input from the user. Check whether the two numbers are equal or not using NOT operator. Hint: (a != b)
Slide 5 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	* Watch the video available at the following link It summarises the Spoken Tutorial project If you do not have good bandwidth, you can download and watch it
Slide 6 Spoken Tutorial Workshops The Spoken Tutorial Project Team Conducts workshops using spoken tutorials Gives certificates for those who pass an online test For more details, please write to contact@spoken-tutorial.org	The Spoken Tutorial Project Team * Conducts workshops using spoken tutorials Gives certificates for those who pass an online test For more details, please write to contact at spoken hyphen tutorial dot org
Slide 7 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	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 spoken hyphen tutorial dot org slash NMEICT hyphen Intro
Remain on previous slide No slide for this part	This is Ritwik Joshi from IIT Bombay. Thank you for joining.

Contributors and Content Editors

Ashwini, Nancyvarkey