Unit 4 - Object Oriented Programming / C++

C++ Programming Structures (Part III) QF002/4/1

UNIT4

General Objective : To understand and identify the fundamental concept of repetition structure.

Specific Objective : At the end of the unit you should be able to:-

Recognize the repetition structure.

Differentiate the repetition structure.

Write and design a simple program using the

repetition structure.

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OBJECTIVES

C++ PROGRAMMING STRUCTURES (Part III)


4.0 Repetition Structure

The repetition structure allow a sequence of instructions to

be executed repeatedly until a certain condition is reached.

This structure comes in three forms:

4.1 While Statement

A while structure allows the program to repeat a set of

statements as long as the starting condition remains true.

‘True’ is used in the Boolean sense and so the condition for

the loop to continue must evaluate to true or false.

The program evaluates the condition if it is true then the

statements inside the braces are executed. The condition is

evaluated again. This will continue until the condition is

false and the program jumps to the next line after the body of

the structure. If only one statement is used in the while loop

then the braces are not required.

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INPUT

a.

b.

c. For


The while statement construct has the general form

The expression is first evaluated,

If it is TRUE the statement block is executed

If it is FALSE, the statement block is skipped

Figure 4.2: Flowchart Of While Statement Structure

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While (expression) statement block;

Figure 4.1: A While Statement Structure

exp Statement

No

Yes

A while structure allows the program to repeat as long as the condition remains true

Ahha.. Error?


Here is an example of the programming using while statement

2: // while statements3:4: #include <iostream.h>5:6: int main()7: {8: unsigned short small;9: unsigned long large;10: const unsigned short MAXSMALL=65535;11:12: cout << "Enter a small number: ";13: cin >> small;14: cout << "Enter a large number: ";15: cin >> large;16:17: cout << "small: " << small << "...";18:19: // for each iteration, test three conditions20: while (small < large && large > 0 && small < MAXSMALL)21:22: {23: if (small % 5000 == 0) // write a dot every 5k lines24: cout << ".";25:26: small++;27:28: large-=2;29: }30:31: cout <<"\nSmall:"<< small << " Large:" << large <<endl;32: return 0;33: }

Figure 4.3: An Example Of While Statement Structure

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Analysis: This program is a game. Enter two numbers, one

small and one large. The smaller number will count up by

ones and the larger number will count down by twos. The

goal of the game is to guess when they will meet.

In lines 12-15, the numbers are entered. Line 20 sets up a

while loop which will continue only as long as three

conditions are met small is not bigger than large; large isn't

negative and small doesn't overrun the size of a small integer

(MAXSMALL).

In line 23, the value in small is calculated modulo 5,000.

This does not change the value in small; however, it only

returns the value 0 when small is an exact multiple of 5,000.

Each time a dot (.) is printed to the screen to show progress.

In line 26, small is incremented and on line 28, large is

decremented by 2.

When any of the three conditions in the while loop fails, the

loop ends and execution of the program continues after the

while loop's closing brace in line 29.

An Output of the program

Output: Enter a small number: 2Enter a large number: 100000small: 2.........Small: 33335 Large: 33334

Figure 4.4 :An Output Of While Statement Structure

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4.2 Do- while statement

A variation on the simple while loop is the do while

structure. The do part contains the body and is executed as

long as the while condition remains true.

The difference between these two while structures are that

with a simple while loop the condition is evaluated first

and if it is immediately false, the body is never executed. In

the do while loop, the body is executed before the condition

is tested and so guaranteed to be executed at least once.

Figure 4.5 below shows the general form of do-while

structure

Figure 4.5: A Do- While Statement Structure

Figure 4.6: A Do- While Statement Structure

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Do Statement block

While (expression);

exp

Statement

No

Yes


A simple program

// Program to illustrate a do while loop

#include <ios.stream.h>

void main()

{

int selection;

do

{

cout << “\n Menu\n”;

cout << “\n 0. Exit\n”;

cout << “\n 1. Append\n”;

cout << “\n 2. Delete\n”;

cout << “\n 3. Modify\n”;

cout << “\n\n Enter Selection: ”;

cin >> selection;

} while(selection >0 && selection < 4);

// The do loop is repeated if the expression is

true

}

Figure 4.7 : A Do- While Statement Structure

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The main difference is that in the while statement, the conditional expression is evaluated at the top of the loop, while in the do-while statement, the conditional expression is evaluated at the bottom of the loop. Therefore, the statements controlled by the do-while statement are executed at least once.

What is the difference between the while and do-while statements?


An Output of a simple Program

Figure 4.8 An Output Of Do-While Statement Structure

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In the Do- while loop, the body is executed before the condition is tested and executed at lest one

In the While loop the condition is evaluated first and if it is immediately false, the body is never executed


Test your comprehension before continuing the next input.Check your answers on the next page.

4.1 What is repetition structure?

4.2 Name the components of the repetition structure.

4.3What is the main difference between the while and do-while

statements?

4.4 Can the while statement end with a semicolon?

4.5Develop a simple program to print cubes by using while

statement

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Activity 4a


Make sure you have tried to answer all the questions given.you can

check your answers with the answers below.

4.1. The repetition structure permits a sequence of the instructions to

be executed repeatedly until a certain condition is reached.

4.2. The components of repetition structure are:

a. While

b. Do- while

c. For

4.3. The main difference is that in the while statement, the

conditional expression is evaluated at the top of the loop,

while in the do-while statement, the conditional expression is

evaluated at the bottom of the loop. Therefore the statements

controlled by the do-while statements are executed at least

once.

4.4. By definition, the while statement does not end with a

semicolon. However, it is legal in C to put a semicolon right

after the while statement

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Feedback 4a


4.5. Example of the While structure program :-

#include<iostream.h>

main()

{

int n;

cout<< “Enter positif integers. Terminate with

0.\n\t: “;

cin>>n;

while (n>0) {

cout << n<< “cubed is “ <<n*n*n<<”\n\t:

“;

cin >> n;

}

}

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4.3 For statement

The for structure has the general form as the while structure.

Figure 4.9 A For Statement Structure

The initialization part is used to initialize any variable(s) that

may need to be initialized. This part is performed just once at

the start of the loop.

The expression part determines whether the loop execution

should continue. If the value of the expression is TRUE (non

zero), the statements block will be executed otherwise the loop

will be terminated.

The incremented part typically increments or decrements the

loop index. This performed every time through the loop

iteration. This part is used to increment any variable(s) that

may need to be incremented.

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for(initialization ;expression; incrementation) statement block;

For loop expression is not

terminated with semicolon

Remember that!!!!!

Yes….Sir!!!


A simple program

#include <iostream.h>

void main()

{

int i, sum, sum2;

for (i=2,sum=0,sum2=0;i<=20; i = i+2)

{

sum = sum + i;

sum2= sum2 + i * i;

}

cout << “\n Sum of first 20 even natural numbers = “

<< sum;

cout << “\n Sum of their squares = << sum2;

}

Figure 4.10 An Example Of A Simple Program

Figure 4.11 An Output Of A Simple Program

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4.4 Break And Continue Statement

Two commands that can be included in looping processes are

continue and break. The continue statement, when included in

the body of the loop causes the program to return immediately

to the start of the loop and ignore any remaining part of the

body. The break statement causes the program to immediately

exit from the loop and resume at the next line of the program

4.5 The break statement

The special statement "break" causes the loop to be abandoned

and execution continues following the closing curly brace.

Figure 4.12 A Statement Of Break Statement

The figure above shows the program continues after the end of

the loop. Within a nested loop, "break" causes the innermost

loop to be abandoned.

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while ( i > 0 ) { ....; if ( j == .... ) { break; // abandon the loop } ....; } // end of the loop body

cout << "continues here ...\n";


4.6 The continue statement

The continue statement is to terminate loop but also goes back to the beginning of the loop’s block to begin the next iteration.

An example of a simple program

#include <iostream.h>

main()

{

int n;

for (;;){

cout << “Enter int: “; cin >> n;

if (n%2 = = 0) continue;

else if (n%3 = = 0) break;

cout << “\t Bottom of loop.\n”;

}

cout << “\t Outside of loop.\n”;

}

Figure 4.12 An Example Of A Simple Program

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Kamal… what can the continue statement do inside a loop ?

Sh…. When the continue statement inside a loop is executed, the program control is branched back to the beginning of the loop so that another iteration can be started.Emmm…..


An output of a simple program

Figure 4.13 An Output Of A Simple Program

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The go to statement enables the computer to jump to same other spot in your computer.


Test your comprehension before continuing the next inputCheck your answers on the next page.

4.6. What is break statement used for?

4.7. What is continue statement used for?

4.8. Write a simple program using for statement to calculate the square root of even number.

4.9. What can the continue statement do inside a loop?

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Activity 4b


Make sure you have tried to answer all the questions given. You can check your answers with the answers below

4.6. The break statement is used to terminate the switch

construct or a loop.

4.7. The continue statement is used to let you stay within a loop

while skipping over some statements.

4.8.

main()

{

float x;

cout << “Enter a positive number: ”;

cin >> x;

for (int n = 1; n * n <= x, n++)

;

cout <<“The integer square root of“ << x >>“is”

<< n – 1 << endl;

}

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Feedback 4b


4.9.When the continue statement inside a loop is executed, the

program control is branched back to the beginning of the loop

so that another iteration can be started. Inside the loop, any

statements following the continue statement will be skipped

over each other if the continue statement is executed.

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The while structure allows the program to repeat a set of statements as long as the starting condition remains true.

In the do-while statemant, the conditional expression is evaluated at the bottom of the loop.

The Do- while loop, the body is executed before the condition is tested and executed at lest one.

The break statement causes the loop to be abandoned and execution continues following the closing curly brace.

The continue statement is to terminate loop but also goes back to the beginning of the loop’s block to begin the next iteration.

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Key Facts


You are approaching success, please answer the questions below. If you

have any problems, please discuss it with your lecturer. Wish you good

luck and all the best.

Question 4-1

a. Is it possible to nest while loops within for loops?

b. Is it possible to create a loop that never ends? Give an example.

c Write a while loop to count from 100 to 200 by 2s.

d. Write a do...while loop to count from 100 to 200 by 2s.

e. What is wrong with this code?

int counter = 0

while (counter < 10)

{

cout << "counter: " << counter;

counter++;

}

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Self-Assessment


f. What is wrong with this code?

int counter = 100;

while (counter < 10){

cout << "counter now: " << counter;

counter--;}

Question 4-2.

a. How do I initialize more than one variable in a for loop?

b. Why is goto should be avoided?

c. Is it possible to write a for loop with a body that is never

executed?

d. What is the value of x when the for loop completes?

for (int x = 0; x < 100; x++)

e. Write a nested for loop that prints a 10x10 pattern of 0s.

f. Write a for statement to count from 100 to 200 by 2s.

for (int x = 100; x<=200; x+=2)

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g. What wrong with this code?

for (int counter = 0; counter < 10; counter++);

cout << counter << "\n";

h. What wrong with this code?

cout << "Enter a number between 0 and 5: ";

cin >> theNumber;

switch (theNumber)

{

case 0:

doZero();

case 1: // fall through




case 5:

doOneToFive();

break;

default:

doDefault();

break;

}

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Make sure you have tried to answer all the questions given. You can

check your answers with the answers below.

Answer 4-1

a. Yes. Any loop can be nested within any other loops.

b. Yes. Following are examples for both a for loop and a while

loop:

for(;;)

{

// This for loop never ends!

}

while(1)

{

// This while loop never ends!

}

c

int x = 100;

while (x <= 200)

x+= 2;

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Feedback On Self-assessment


d.

int x = 100;

do

{

x+=2;

} while (x <= 200);

e.

int counter = 0

while (counter < 10)

{

cout << "counter: " << counter;

counter++;

}

The counter is never incremented and the while

loop will never terminate.

f.

int counter = 100;

while (counter < 10){

cout << "counter now: " << counter;

counter--;}

The counter is initialized to 100, but the test condition is that if it is

less than 10, the test will fail and the body will never be executed. If

line 1 were changed to int counter = 5;, the loop would not terminate

until it had counted down past the smallest possible int. Because int

is signed by default, this would not be what has been intended.

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Answer 4-2.

a. Separate the initializations with commas, such as

for (x = 0, y = 10; x < 100; x++, y++)

b. goto jumps in any direction to any arbitrary line of code. This

makes for source code that is difficult to understand and therefore

difficult to maintain.

c. Yes, if the condition is FALSE after the initialization, the body of

the for loop will never execute. Here's an example:

for (int x = 100; x < 100; x++)

d. 100

e.

for (int i = 0; i< 10; i++)

{

for ( int j = 0; j< 10; j++)

cout << "0";

cout << "\n";

}

f.

for (int x = 100; x<=200; x+=2)

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g.

for (int counter = 0; counter < 10;

counter++); cout << counter << "\n";

There is a semicolon after the loop, and the loop does nothing.

The programmer may have intended this, but if counter was

supposed to print each value, it won't.

h. Case 0 probably needs a break statement. If it does not, it should be

documented with a comment

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CONGRATULATIONSMay success be with you always……..

Unit 4 - Object Oriented Programming / C++

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