Looping c الفصل الثانى

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Starting Out with C++, 3rdEdition

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The Increment and Decrement Operators

++ and -- are operators that add and subtract

one from their operands.

num = num + 1;

num += 1;

num++;


2

Program 5-1// This program demonstrates the increment and decrement

// operators.

#include

void main(void)

{

int bigVal = 10, smallVal = 1;

cout

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Program 5-2

//This program demonstrates the prefix and postfix modes of the

// increment and decrement operators.

#include

void main(void)

{

int bigVal = 10, smallVal = 1;

cout

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5.2 Introduction to Loops - The while

Loop

A loop is part of a program that repeats.

A while loop is a pre test loop - the

expression is tested before the loop is

executed

while (expression)

statement;


10

Program 5-3// This program demonstrates a simple while loop.

#include

void main(void)

{

int number = 0;

cout number;}


11

Program Output with Example Input

This program will let you enter number after number. Enter

99 when you want to quit the program.

1 [Enter]

2 [Enter]

30 [Enter]

75 [Enter]

99 [Enter]


12

Terminating a Loop

A loop that does not have a way of stopping is called

an infinite loop

int test = 0;

while (test < 10)

cout

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Programming Style and the while Loop

If there is only one statement repeated by

the loop, it should appear on the line after

the while statement and be indented one

additional level

If the loop repeats a block, the block shouldbegin on the line after the while statement

and each line inside the braces should beindented


14

5.3 Counters

A counter is a variable that is incremented

or decremented each time a loop iterates.


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Program 5-4

// This program displays the numbers 1 through 10 and

// their squares.

#include

void main(void)

{

int num = 1; // Initialize counter

cout

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Program 5-5

// This program displays the numbers 1 through 10

and

// their squares.

#include

void main(void)

{

int num = 0;

cout

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Program continued from previous slide.

while (count++ < numStudents)

{

int score1, score2, score3;

float average;

cout > score2 >> score3;

average = (score1 + score2 + score3) / 3.0;

cout

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Program continues

while (count++ < days)

{

float sales;

cout

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while (points != -1)

{

count++;

cout > score3;

average = (score1 + score2 + score3) / 3.0;

cout

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Program Output w ith Example Input

Enter 3 scores and I will average them: 80 90 70 [Enter]

The average is 80.

Do you want to average another set? (Y/N) y [Enter]

Enter 3 scores and I will average them: 60 75 88 [Enter]

The average is 74.333336.

Do you want to average another set? (Y/N) n [Enter]


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The for Loop

Ideal for situations that require a counter

because it has built-in expressions that

initialize and update variables.

for (initialization; test; update)

statement;


35

Program 5-11// This program displays the numbers 1 through 10 and

// their squares.

#include

void main(void)

{

int num;

cout

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Omitting the for Loops Expressions

int num = 1;

for ( ; num

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Program Output with Example Input

Enter the sales for day 1: 489.32 [Enter]







The total sales are $3413.71


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5.8 Other forms of the update

expression

Incrementing the counter by something besides 1:for(number = 2; number

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Program 5-13

// This program averages test scores. It asks the user for the

// number of students and the number of test scores per student.

#include

void main(void)

{

int numStudents, numTests, total;

float average;

cout numStudents;

cout > numTests;

Program continues


46


for (int count1 = 1; count1

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Program 5-14// This program raises the user's number to the powers

// of 0 through 10.

#include

#include

void main(void)

{

int value;

char choice;

cout > value;

cout

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