Difference between revisions of "Digital-Divide/D0/How-to-apply-for-a-PAN-Card/English"

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.

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 )

{

statement block

}

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 );

I have already typed the code on the editor.

So will just open it.

loops.c

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

#include <stdio.h>

int main()

int x=0;

int y=0;

while(x<=10)

{

y+=x;

x++;

}

The value obtained after the addition is stored in y.

I will explain it after the while loop.

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

return 0;

Ctrl, Alt and T keys simultaneously

gcc loops.c -o loop

To execute

Type

./loop

gcc loops.c -o loop

To execute,

Type

./loop

Output 55

55

do

{y+=x;

x++;}

while(x<=10);

y+=x;

The value obtained after the addition is stored in y.

x++;

Compile and execute

55

If the condition is false, then the body of the loop will not be executed.

While condition does not ends with a semicolon.

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.

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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