C-and-C++/C3/Loops/English

Title of script: Loops in C and C++

Author: Dhawal Goyal

Keywords: Loops, for loop, while loop, do....while loop, type casting, and Video tutorial

Visual Cue	Narration
Slide 1	Welcome to the spoken tutorial on Loops in C and C++
Slide 2	In this tutorial we will learn, for loop, while loop and do…while loop. We will do this with the help of examples. We will also see some common errors and their solutions.
Slide 3	To record this tutorial, I am using Ubuntu Operating System version 11.04 gcc and g++ Compiler version 4.6.1 on Ubuntu.
Slide 4	Now let us start with the introduction to loops. Loops are used to execute a group of instructions repeatedly.
Slide 5	Depending on the purpose they are divided into three types: while loop do…..while loop for loop
Slide 6	Let us start with the while loop A while loop tests the condition in the beginning The structure is as follows while ( condition ) { statement block }
Slide 7	Now move on to the do….while loop A do..while loop is executed at least once before the condition could be validated. The structure is as follows do { statement block } while ( condition );
	Let us see an example on while and do...while loop in C. I have already typed the code on the editor. So will just open it.
Point the cursor loops.c	Please note that I have saved the file with the name loops.c. Today we are going to learn addition of first 10 numbers.
Highlight #include <stdio.h>	This is our header file.
Highlight int main()	This is our main function.
Highlight int x=0; int y=0;	The variable x and y are declared and initialized to 0.
	First we will look at the while loop.
Highlight the while loop while(x<=10) { y+=x; x++; }	This is the while loop.
Highlight while(x<=10)	The condition of the while loop is x is less than or equal to 10.
Highlight y+=x;	Here the value of x is added to the value of y. The value obtained after the addition is stored in y.
Highlight x++;	Here the variable x is increased by one.
Highlight the commented do….while loop	I have commented the do-while loop here. I will explain it after the while loop.
Highlight printf( "%d\n", y );	Here we print the value of y.
Highlight return 0;	This is our return statement.
Click on Save	Now Click on Save.
	Let us execute.
Open the terminal Ctrl, Alt and T keys simultaneously	Open the terminal by pressing Ctrl, Alt and T keys simultaneously.
Type gcc loops.c -o loop To execute Type ./loop	To compile the program, type gcc loops.c -o loop To execute, Type ./loop
Highlight Output 55	Here the output is displayed as 55
	Now, we will look at the same example with do….while loop
Switch to the editor	Let us again switch to loops.c
Comment the while loop and uncomment the do….while loop	Comment the while loop and uncomment the do….while loop
Highlight do {y+=x; x++;} while(x<=10);	The structure of the do….while loop is different.
Highlight y+=x;	Here the value of x is added to the value of y The value obtained after the addition is stored in y.
Highlight x++;	Here the variable x is increased by one.
Highlight while ( x <= 10 );	Now we check the condition whether x is less than or equal to 10.
Click on Save	Now Click on Save.
	Switch back to the terminal.
Switch to terminal Compile and execute	Let us compile and execute the program as before.
Highlight 55	Here the output is displayed as 55
	Come back to our program.
	Here, we can see, in while loop the condition is checked first. If the condition is false, then the body of the loop will not be executed. While condition does not ends with a semicolon.
	In do-while loop the condition is checked at the end. Here, if the condition is false, Then also the body of the loop is executed once. Here the body of the loop is executed once. Then the condition is checked. In do-while loop the while condition is ends with a semicolon.
On the editor	NOW LET US SEE HOW TO EXECUTE THESE PROGRAMS IN C++ I have already made the program. So lets take a look at it.
Point the cursor at loops1.cpp	Please note that I have saved the file with the name loops1.cpp
Highlight #include<iostream>	This is our header file iostream.
Highlight using namespace std;	This is the using statement.
Highlight int main()	This is the main function.
Highlight int x=0; int y=0;	Here the variables x and y are declared and initialized to 0.
Highlight structure of while loop while(x<=10) { y+=x; x++; }	The structure of the while loop is the same for C++ as in C
Highlight the commented do….while loop	The do….while loop is already commented
Highlight cout<<y<<”\n”;	Here we print the value of y.
Highlight return 0;	This is the return statement.
Click on Save	Now click on Save.
On the terminal	Let us compile Come back to the terminal
Type g++ loops1.cpp -o loop1 Type ./loop1	Type g++ loops1.cpp -o loop1 press Enter To execute Type ./loop1
Highlight Output	Here the output is displayed as 55
Switch to the editor	Now let us see the do….while loop Go back to the editor
Uncomment do….while loop and comment while loop	Let us uncomment the do….while loop and comment the while loop
Highlight do….while loop do {y+=x; x++;} while(x<=10);	The structure of the while loop is the same for C++ as in C.
Highlight cout<<y<<”\n”;	Here we print the value of y.
Click on Save	Now Click on Save.
Switch to terminal Compile and execute	Come back to the terminal Let us compile and execute as before.
Highlight 55	Here the output is displayed as 55
Error 1	Now let us see some of the common errors which we can come across. We switch to the editor and open loops1.cpp
int x=0;	Now we look at the while loop. Suppose we do not declare the variable x outside the while loop. I will remove int x=0; from line no.6 And add it inside the while loop after line no.9 I will retain rest of the code as it is. Save the program
Switch to the terminal Compile and execute	Let us go to the terminal, compile and execute the program again.
Highlight error Highlight Line no.8 Highlight loops1.cpp Highlight x undeclared	We see that there is an error at line no.8 in our loops1.cpp file Variable x undeclared.
Erase int x=0; from line no.10 and rewrite int x=0; at line no.6	Come back to our program x should not be declared inside the loop. Remove int x=0; from line no.10. Rewrite it outside the loop at line no.6 as before Click on Save
Switch to the terminal Compile and execute	Let us go back to the terminal Compile and execute the program.
	Yes, it’s working. Let us get back to our slides.
	This brings us to the end of tutorial on loops.
Slide 10 Summary	In this tutorial we learned, while loop eg. while(x<=10) do….while loop eg. do {….} while(x<=10);
Slide 11	As an assignment Write a program to print the following using all the loops 0 1 2 3 4 5 6 7 8 9 Hint: the syntax of the for loop is for (var initialization; condition; var incre\decre) { body }
Highlight/point the mouse on variable initialization;	Here we initialize the variable
Highlight/point the mouse on condition;	Here we write the condition for the loop
Highlight/point the mouse on variable update	Here we update the variable
Highlight/point the mouse on { body }	Here we write the body of the loop
Slide 12 About the Spoken Tutorial Project	Watch the video available at the link shown It summarizes 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 Number 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: http://spoken-tutorial.org\NMEICT-Intro
	This is Dhawal Goyal from IIT Bombay signing off Thank You for joining.

Contributors and Content Editors

Ashwini, Nancyvarkey