Difference between revisions of "C-and-C++/C3/Loops/English"

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.

Ubuntu Operating System version 11.04

gcc and g++ Compiler version 4.6.1 on Ubuntu.

Loops are used to execute a group of instructions repeatedly.

while loop

do…..while loop

for loop

A while loop tests the condition in the beginning.

The structure is as follows

while ( condition )

{ (within the brackets)

statement block

}

A do..while loop is executed at least once before the condition could be validated.

The structure is as follows

do { (within the brackets)

statement block

} (after the brackets)

while ( condition );

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

I have already typed the code on the editor.

Let me open it.

while.c

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

Let me explain the code now.

#include <stdio.h>

int main()

{

int x=0;

int y=0;

And initialized to 0.

while(x<=10)

{

y+=x;

x++;

}

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

The value obtained after the addition is stored in y.

Then we print the value of y.

That means the variable x is increased by one.

return 0;

Ctrl, Alt and T keys simultaneously

gcc while.c -o while

To execute,

Type

./while

gcc while.c -o while

To execute,

Type

./while

Output 55

Let me resize the windows.

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.

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.

y+=x;

The value obtained after the addition is stored in y.

Now let us execute the program.

Type:

gcc do-while.c -o do

Type:

./do

gcc do-while.c -o do

Type:

./do

Output

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

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.

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.

I have already made the program.

So lets take a look at it.

#include<iostream>

using namespace std;

int x=0;

int y=0;

while(x<=10)

{

y+=x;

x++;

}

Come back to the terminal

g++ loops1.cpp -o loop1

Type

./loop1

g++ loops1.cpp -o loop1

press Enter

To execute

Type

./loop1

Output

55

Go back to the editor

do

{y+=x;

x++;}

while(x<=10);

cout<<y<<”\n”;

Compile and execute

Let us compile and execute as before.

55

We switch to the editor and open loops1.cpp

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

Compile and execute

Highlight Line no.8

Highlight loops1.cpp

Highlight x undeclared

Variable x undeclared.

from line no.10

and rewrite int x=0;

at line no.6

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

Compile and execute

Compile and execute the program.

Let us get back to our slides.

Summary

while loop

eg. while(x<=10)

do….while loop

eg. do

{….}

while(x<=10);

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

}

{

body

}

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