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-

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-

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

Type

./while

gcc while.c -o while

Press Enter.

Type ./while

Press Enter.

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

Press Enter.

Type: ./do

Press Enter.

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.

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

Highlight

#include<iostream>

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

We have included the using statement here:

using namespace std;

using namespace std;

cout<<

while(x<=10)

{

y+=x;

x++;

}

Come back to our terminal.

Press Enter

type ./while1 Press Enter

Press Enter.

Type ./while1

Press Enter.

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

Come back to our text editor.

Let us execute the program.

Come back to our terminal.

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

type ./do1 Press Enter

Press Enter

Type ./do1

Press Enter.

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

Output

Come back to our text editor.

Click on Save.

Come back to our terminal.

Compile and execute

Let us execute the program again.

Press the up arrow key.

Again press the up-arrow key.

Highlight Line no.8

Highlight loops1.cpp

Highlight x undeclared

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.

from line no.10

and rewrite int x=0;

at line no.6

Let us fix the error.

Type x++ and a semicolon.

Click on Save

Let us execute again.

Compile and execute

Press the up-arrow key.

Yes, it is working.

We will move back to our slides.

Summary

In this tutorial we learned,

• 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

}

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