CS-1301

Lecture 7

Repetition Structure

Department of Computer Science

College of Arts and Science

Mr. Asad Abd Elrashid

a.Khalil@psau.edu.sa

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Content

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Introduction.

For loop.

While loop.

Do-while loop.

Challenge.

Introduction

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Loops are used to execute any part of program

repeatedly.

Types of loops

For While Do - while

For loop

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The most important looping structure in C++.

General syntax of :

for (initial ; condition ; increment )

statement or statements ;

initial, condition, and increment are C++ expressions.

Cont..

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• For loops are executed as follows:

1. initial is evaluated. Usually an assignment statement.

2. condition is evaluated. Usually a relational expression.

3. If condition is false (i.e. 0), fall out of the loop (go to step 6.)

4. If condition is true (i.e. nonzero), execute statement

5. Execute increment and go back to step 2.

6. Next statement

Ways to write for loop

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#include <iostream.h>

int main () {

int count,x,y;

int ctd;

/* 1. simple counted for loop */

for (count =1; count <=20; count++)

cout<<“\n"<<count;

/* 2. for loop counting backwards */

for (count = 100; count >0; count--) {

x*=count;

cout<<"count=“<<count<<“x=“<<x<<“\n";

}

Cont..

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/* 3. for loop counting by 5's */

for (count=0; count<1000; count += 5)

y=y+count;

/* 4. initialization outside of loop */

count = 1;

for ( ; count < 1000; count++)

cout<< count;

Cont..

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/* 5. very little need be in the for */

count=1; ctd=1;

for ( ; ctd; ) {

cout<<count;

count++; ctd=count<1000;

}

/* 6. compound statements for initialization and increment */

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

cout<< x<<y <<”\n";

}

return 0;

}

Example (1)

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* Demonstrates a simple for statement */

#include <iostream.h>

int count;

int main( void )

{

/* Print the numbers 1 through 20 */

for (count = 1; count <= 20; count++)

cout<<count<<"\n";

return 0;

}

Example (2)

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Write a C++ program to print numbers from(1 - 5)?

#include <stdio.h>

int i;

int main( )

{

/* Print the numbers 1 - 5 */

for (i=1;i<6;i++)

cout<<i;

return 0;

}

Challenge

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Write a C++ program to print numbers from(5 - 1) by

using for loop?

Example(3)

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Write a C++ program to print numbers from(1 - 10) by using

for loop?

#include <iostream.h>

#include <conio.h>

int i;

int main( void )

{

for (i=1;i<=10;i++)

{ cout<<"\n”<< i;

cout<<"\t\t”<<i*i<<”\n";}

getch();

return 0;

}

While loop

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General syntax of :

while (condition)

{

statement;

Increment or decrement;

}

Cont..

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Executes as expected:

1. condition is evaluated

2. If condition is false (i.e. 0), loop is exited (go to

step 5)

3. If condition is true (i.e. nonzero), statement is

executed

4. Go to step 1

5. Next statement

Cont..

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Note:for ( ; condition ; ) is equivalent to while (condition)

stmt; stmt;

for (exp1; exp2; exp3) stmt;

is equivalent to

exp1;

while(exp2) { stmt; exp3; }

Example(4)

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#include <iostream.h>

int n,i=0,sum=0;

int main( )

{cout<<“enter the limits:\n”;

cin>>n;

while(i<=n){

cout<<i;

sum = sum+i;

i++;}

return 0;

}

Do - while loop

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General syntax of :

do

{

Statement or statements;

increment or decrement;

}

while(condition );

Example

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#include <iostream.h>

char ch=’ ’;

int a,b=0;

int main( )

do{

cout<<“enter any two integer numbers:\n”;

cin<<a<<b;

cout<<“sum=“<<a+b<<“\n”;

cout<<“Do you want to continue (Y/N):\n”);

cin>>ch;

}while(ch != ‘n’)

return 0;}

challenge

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1- Change the previous program to work with while

loop?

Thank you for your attention

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Lecturer : Aasd Abd Elrashid