Overview

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# Overview - PowerPoint PPT Presentation

Overview. do/while loop break statement continue statement switch statement. do/while loop. do { statement; } while (condition); Step1: Execute statements inside braces Step2: Evaluate condition. Step3: If condition is true repeat Step1 through 3, otherwise

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Presentation Transcript
Overview
• do/while loop
• break statement
• continue statement
• switch statement
do/while loop

do {

statement;

} while (condition);

Step1: Execute statements inside braces

Step2: Evaluate condition.

Step3: If condition is true repeat Step1 through 3, otherwise

continue execution at next statement following the do/while

statement

Usually use { } even when not necessary

Useful when you want the statements to execute at least once.

do while example

do {

cout << “Enter a number between 1 and 10: “;

cin >> number;

} while (number <= 0 || number > 10);

do/while example

What will the output of the following program sequence be?

int j = 4;

do {

j = j - 2;

cout << “Hi”;

} while (++j > 0);

Walk through this example showing how j changes.

Loop Exercises

1) How many times does the statement inside the do/while

body execute? What gets displayed?

int i = 0, x = 2;

do {

x = x + i;

} while (++ i < 3);

cout << “x = “ << x << endl;

2) How many times does the cout statement execute?

for (int i = 1; i <= 4; i++) {

for (int j = 1; j <= 3; j++) {

cout << “Hello” << endl;

}

}

continue statement

skip the rest of this iteration and continue with the next iteration of the loop

int x = 1;

while ( x <= 10) {

if (5 == x) {

x++;

continue;

}

cout << x << endl;

x++;

}

condition (x <= 10) is next statement executed after the continue statement.

continue statement
• for (int x = 1; x <= 10; x++) {
• if (5 == x)
• continue;
• cout << x << endl;
• }
• next statements executed after continue are
• x ++;
• x <= 10;
break statement
• Breaks out of the loop. Next statement executed after a
• break statement is the statement immediately following the loop.
• for (int x = 1; x <= 10; x++) {
• if (5 == x)
• break;
• cout << x << endl;
• }
• Next statement executed after the break statement is the
• statement immediately following the for loop.
else if example

gpa = 4.0;

gpa = 3.0;

gpa = 2.0;

gpa = 1.0;

gpa = 0.0;

else

cout << “Illegal letter grade” << endl;

switch statement

case ‘A’:

gpa = 4.0;

break;

case ‘B’:

gpa = 3.0;

break;

case ‘C’:

gpa = 2.0;

break;

case ‘D’:

gpa = 1.0;

break;

case ‘F’:

gpa = 1.0;

break;

default:

cout << “Illegal letter grade” << endl;

}

switch statement syntax

switch (controlling expression) {

case label1: statement(s);

break;

case label2: statement(s);

break;

.

.

.

case labeln: statement(s);

break;

default: statement(s);

}

switch statement rules
• controlling expression must be of type int or char
• labels must be constants that match the type of the controlling expression
• default statement can be anywhere. More intuitive at bottom.
• can have multiple case labels sharing the same code

case ‘A’: case ‘a’ :

statements;

break;

else if that cannot be implemented as a switch

int score;

cout << “Enter score: “;

cin >> score;

if (score < 68)

cout << “NR” << endl;

else if (score < 78)

cout << “C” << endl;

else if (score < 88)

cout << “B” << endl;

else

cout << “A” << endl;

common programming errors
• Forgetting the break statement. Statements for next case get executed by mistake.
• Forgetting the space between the word case and the label. Will not be flagged by compiler but won’t execute the way you intend.
Grandma’s Attic

for (char letter = \'a\'; letter <= ‘i\'; letter++) {

cout << "I\'m going to Grandma\'s attic and I\'m going to get ";

switch (letter) {

case \'i\': cout << "an igloo, ";

case \'h\': cout << "a hat, ";

case \'g\': cout << "a goat, ";

case \'f\': cout << "a fox, ";

case \'e\': cout << "an elephant, ";

case \'d\': cout << "a dinosaur, ";

case \'c\': cout << "a cookie, ";

case \'b\': cout << "a ball and ";

case \'a\': cout << "an apple" << endl;

default: break;

}

}