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

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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 some 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 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 and
  • for loop
Slide 6 Let us start with the while loop first.

A while loop tests the condition in the beginning.

The structure is-

while ( condition )

{ (within the brackets)

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-

do { (within the brackets)

statement block

} (after the brackets)

the while ( condition );


You can see that the condition is checked at the end.

Now let us see an example on while and do...while loop.

I have already typed the code on the editor.

Let me open it.

Point the cursor

while.c

Note that our filename is while.c

Today we are going to learn addition of first 10 numbers using while loop.

Let me explain the code now.

Highlight

#include <stdio.h>

This is our header file.
Highlight

int main()

{

int x=0;

int y=0;

Inside the main function we have declared two integer variables x and y.

And initialized to 0.

Highlight the while loop

while(x<=10)

{

y+=x;

x++;

}

This is our while loop.
Highlight while(x<=10) The condition of the while loop is x is less than or equal to 10
Highlight y+=x;

printf( "%d\n", y );

Here the value of x is added to the value of y.

The value obtained after the addition is stored in y.

Then we print the value of y.

Highlight x++; Here x is incremented.

That means the variable x is increased by one.

Highlight

return 0;

And this is our return statement.
Now let us execute the program.
Open the terminal

Ctrl, Alt and T keys simultaneously

Please open the terminal by pressing Ctrl, Alt and T keys simultaneously on your keyboard.
Type

gcc while.c -o while

Type

./while

Type

gcc space while.c space -o space while

Press Enter.

Type ./while

Press Enter.

Highlight

Output 55

The output is displayed.


Now let us see the working of while loop.

Let me resize the windows.

Highlight the output. Here 1st the value of x and y is 0.
Highlight the output. This is our while condition.

Here we check whether the value of x is less than or equal to 10.

Which means the values of x will be from 0 to 10.

Then we add y + x ie 0 + 0

We get 0.

We print the value of y

Here we get 0.

Then x is incremented.

Which means now the value of x will be 1.

Then we will check the condition again.

1 is less than or equal to 10.

If the condition is true, then we will add the values.

y ie 0; + x ie 1.

0+1 is 1.

We print the value as 1.

Again x is incremented.

Now the value of x is 2.

We check the condition again.

2 is less than or equal to 10

If the condition is true, then we will add the values

ie 1+2 which will give 3.

We print the value as 3.

Like this it will go on upto x is less than or equal to 10.

Now, we will see the same program using do….while loop
Point the cursor to the filename. Here is our program. Note that our fielname is do-while.c
Highlight the part. This part is already explained in the previous program.

So let us move on to our do-while loop.

Here first the body of the loop will be executed and then the condition is checked.

Highlight

y+=x;

The value of x is added to the value of y

The value obtained after the addition is stored in y.

The logic is same as in while program.

Now let us execute the program.

On the terminal. Come back to our terminal.


Switch to terminal

Type:

gcc space do-while.c space -o space do

Type:

./do

Type: gcc space do-while.c space -o space do

Press Enter.

Type: ./do

Press Enter.

Highlight

Output

We can see that the output is similar to our while program.

Now let us see the working of do-while loop.

Let me resize the windows.
Highlight the output. Here the value of x and y is 0.

We add those values.

Then we will get 0.

Now the value of y is 0

We print the value as 0.

Then x is incremented by 1.

Which means now the value of x is 1.

Then the condition will be checked.

You can see that the body of the loop is executed first.

Anyhow if the condition is false, then also we will get a value ie 0.

Now here we will check whether 1 is less than or equal to 10.

The condition is true, again we will add the values.

Now 0+1

Then we print the value of y as 1.

Highlight the output. Again, x will be incremented.

Now the value of x is 2.

Then we check 2 is less than or equal to 10.

We will go back here.

Then we will add the values.

1+2 is 3.

We print the value of y as 3.

Like this, the conditions will be checked till the value of x will be less than or equal to 10.
Highlight return 0; And this is our return statement.
Highlight the semicolon Note that here, the while condition ends with a semicolon.
In while loop, the condition does not ends with a semicolon.
On the editor NOW LET US SEE HOW TO EXECUTE THESE PROGRAMS IN C++

This is our while program in C++.

The logic and implementation are same as in our C program.

Point the cursor at while.cpp

Highlight

#include<iostream>

There are a few changes.

Like the header file as iostream in place of stdio.h

We have included the using statement here:

using namespace std;


And here we have used cout function in place of printf function.
Highlight structure of while loop.

while(x<=10)

{

y+=x;

x++;

}

The structure of while loop is same as in our C program.
On the terminal. Let us execute the program.

Come back to our terminal. Let me clear the prompt.

type: g++ space while.cpp space -o space while1

Press Enter

type ./while1 Press Enter


To execute type g++ space while.cpp space -o space while1

Press Enter.

Type ./while1

Press Enter.

You can see that the output is similar to our while program in C.

Highlight the filename do….while loop Now let us see the do….while program in C++

Come back to our text editor.


Highlight return 0; Here also there are similar changes like the header file, the using statement and the cout function.
Click on Save Rest of the things are similar.

Let us execute the program.


Come back to our terminal.

On the terminal

type g++ space do-while.cpp space -o space do1 Press Enter

type ./do1 Press Enter

Type g++ space do-while.cpp space -o space do1

Press Enter

Type ./do1

Press Enter.

We can see that the output is similar to our do-while program in C.

Highlight

Output

Now, we will see some common errors and their solutions.


Switch to the editor

Come back to our text editor.

int x=0; Suppose here, I will not increment the value of x.

Click on Save. Let us see what happens.

Come back to our terminal.

Switch to the terminal

Compile and execute

Let me clear the prompt.

Let us execute the program.

Press the up arrow key twice.

Again press the up-arrow key.

Highlight error

Highlight Line no.8

Highlight loops1.cpp

Highlight x undeclared

The output is displayed.

We can see a number of zeros.

This is because the loop does not have a terminating condition. It is known as infinite loop.

Infinite loop can cause the system to become unresponsive.

It causes the program to consume all the processors time.

But it can be terminated.

Erase int x=0;

from line no.10

and rewrite int x=0;

at line no.6

Come back to our program.

Let us fix the error.

Type x++ and a semicolon.

Click on Save

Let us execute again.

Switch to the terminal

Compile and execute

Come back to the terminal

Press the up-arrow key.

Yes, it is working.

This brings us to the end of this tutorial.

We will move back to our slides.

Slide 10

Summary

Let us summarize.

In this tutorial we learned,

  • while loop
    • eg. while(x<=10)
  • do….while loop
    • eg. do (statement block) {….} (and while condition at the end) while(x<=10);
Slide 11 As an assignment

Write a program to print the following using for loop

0 1 2 3 4 5 6 7 8 9

Hint: the syntax of the for loop is

for (variable initialization; variable condition; variable increment\decrement)

(And here will be the body of the loop)

{

body

}

Slide 12

About the Spoken Tutorial Project

Watch the video available at the link shown below

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

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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 the link shown below: 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

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