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
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Slide 1 | Welcome to the spoken tutorial on Loops in C and C++ |
Slide 2
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In this tutorial we will learn,
We will do this with the help of some examples. We will also see some common errors and their solutions. |
Slide 3
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To record this tutorial, I am using
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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:
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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) while ( condition );
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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 |
To compile the program, type
gcc space while.c space -o space while Press Enter. Type ./while Press Enter. |
Highlight
Output 55 |
The output is displayed.
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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. |
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y+=x; |
Here 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.
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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 the 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 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 will print the value of y as 1. |
Highlight the output. | Again, x will be incremented.
Now the value of x will be 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; |
Highlight
using namespace std; |
This is the using statement. |
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cout<< |
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. |
type: g++ space while.cpp space -o space while1
Press Enter type ./while1 Press Enter
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Type g++ while.cpp -o while1
Press Enter. Type ./while1 Press Enter. We 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.
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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.
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On the terminal
type g++ space do-while.cpp space -o space do1 Press Enter type ./do1 Press Enter |
Type g++ do-while.cpp -o 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.
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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. Come back to our terminal. |
Switch to the terminal
Compile and execute |
Let me clear the prompt.
Let us execute the program again. Press the up arrow key. 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 processer 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,
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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 } |
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
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The Spoken Tutorial Project Team
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Slide Number 14
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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. |