1 looping dale/weems/headington. 2 ka/js/p warning l save your work often! l in the khan academy,...
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DESCRIPTION
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Looping Dale/Weems/Headington
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KA/JS/P Warning
Save your work often!
In the Khan Academy, JavaScript environment, infinite loops will lock up the browser.
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A loop is a repetition control structure.
it causes a single statement or block to be executed repeatedly
What is a loop?
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While StatementSYNTAX
while ( Expression ) { . . // loop body
.}
NOTE: Loop body can be a null statement, or a block.
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When the expression is tested and found to be false, the loop is exited and control passes to the statement which follows the loop body.
WHILE LOOP
FALSE
TRUE bodystatement
Expression
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an initialization of the loop control variable
an expression to test for continuing the loop
an update of the loop control variable to be executed with each iteration of the body
Count-controlled loop contains
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var count ;
count = 4; // initialize loop variable
while (count > 0) // test expression{
println(count); // repeated action
count -- ; // update loop variable}println("Done");
Count-controlled Loop
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Count-controlled Loopvar count ;
count = 4;
while (count > 0){
println(count);
count -- ;}println("Done");
OUTPUT
count
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Count-controlled Loopvar count ;
count = 4;
while (count > 0){
println(count);
count -- ;}println("Done");
OUTPUT
count
4
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Count-controlled Loopvar count ;
count = 4;
while (count > 0) TRUE{
println(count);
count -- ;}println("Done");
OUTPUT
count
4
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Count-controlled Loopvar count ;
count = 4;
while (count > 0){
println(count);
count -- ;}println("Done");
OUTPUT 4
count
4
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Count-controlled Loopvar count ;
count = 4;
while (count > 0){
println(count);
count -- ;}println("Done");
OUTPUT 4
count
3
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Count-controlled Loopvar count ;
count = 4;
while (count > 0) TRUE{
println(count);
count -- ;}println("Done");
OUTPUT 4
count
3
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Count-controlled Loopvar count ;
count = 4;
while (count > 0){
println(count);
count -- ;}println("Done");
OUTPUT 4
3
count
3
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Count-controlled Loopvar count ;
count = 4;
while (count > 0){
println(count);
count -- ;}println("Done");
OUTPUT 4
3
count
2
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Count-controlled Loopvar count ;
count = 4;
while (count > 0) TRUE{
println(count);
count -- ;}println("Done");
OUTPUT 4
3
count
2
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Count-controlled Loopvar count ;
count = 4;
while (count > 0){
println(count);
count -- ;}println("Done");
OUTPUT 4
3 2
count
2
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Count-controlled Loopvar count ;
count = 4;
while (count > 0){
println(count);
count -- ;}println("Done");
OUTPUT 4
3 2
count
1
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Count-controlled Loopvar count ;
count = 4;
while (count > 0) TRUE{
println(count);
count -- ;}println("Done");
OUTPUT 4
3 2
count
1
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Count-controlled Loopvar count ;
count = 4;
while (count > 0){
println(count);
count -- ;}println("Done");
OUTPUT 4
3 2 1
count
1
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Count-controlled Loopvar count ;
count = 4;
while (count > 0){
println(count);
count -- ;}println("Done");
OUTPUT 4
3 2 1
count
0
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Count-controlled Loopvar count ;
count = 4;
while (count > 0) FALSE{
println(count);
count -- ;}println("Done");
OUTPUT 4
3 2 1
count
0
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Count-controlled Loopvar count ;
count = 4;
while (count > 0){
println(count);
count -- ;}println("Done");
OUTPUT 4
3 2 1 Done
count
0
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for Statement
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A Count-Controlled Loop
SYNTAX
for ( initialization ; test expression ; update ) {
0 or more statements to repeat
}
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The for loop contains
an initialization
an expression to test for continuing
an update to execute after each iteration of the body
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Example of Repetition
for ( var num = 1 ; num <= 3 ; num++ ) {
println(num + " Potato");}
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Example of Repetition num
var num;
for ( num = 1 ; num <= 3 ; num++ ) {
println(num + " Potato");
OUTPUT
?
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Example of Repetition num
OUTPUT
1
var num;
for ( num = 1 ; num <= 3 ; num++ ) {
println(num + " Potato");
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Example of Repetition num
OUTPUT
1
var num;
for ( num = 1 ; num <= 3 ; num++ ) {
println(num + " Potato");
true
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Example of Repetition num
var num;
for ( num = 1 ; num <= 3 ; num++ ) {
println(num + " Potato");
OUTPUT
1
1Potato
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Example of Repetition num
OUTPUT
2
var num;
for ( num = 1 ; num <= 3 ; num++ ) {
println(num + " Potato");
1Potato
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Example of Repetition num
OUTPUT
2
true
1Potato
var num;
for ( num = 1 ; num <= 3 ; num++ ) {
println(num + " Potato");
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Example of Repetition num
var num;
for ( num = 1 ; num <= 3 ; num++ ) {
println(num + " Potato");
OUTPUT
2
1Potato
2Potato
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Example of Repetition num
OUTPUT
3
var num;
for ( num = 1 ; num <= 3 ; num++ ) {
println(num + " Potato");
1Potato
2Potato
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Example of Repetition num
OUTPUT
3
true
1Potato
2Potato
var num;
for ( num = 1 ; num <= 3 ; num++ ) {
println(num + " Potato");
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Example of Repetition num
var num;
for ( num = 1 ; num <= 3 ; num++ ) {
println(num + " Potato");
OUTPUT
3
1Potato
2Potato
3Potato
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Example of Repetition num
OUTPUT
4
var num;
for ( num = 1 ; num <= 3 ; num++ ) {
println(num + " Potato");
1Potato
2Potato
3Potato
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Example of Repetition num
OUTPUT
4
false
1Potato
2Potato
3Potato
var num;
for ( num = 1 ; num <= 3 ; num++ ) {
println(num + " Potato");
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Example of Repetition num
When the loop control condition is evaluated and has value false, theloop is said to be “satisfied” and control passes to the statementfollowing the For statement.
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falsevar num;
for ( num = 1 ; num <= 3 ; num++ ) {
println(num + " Potato");
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The output was:
1Potato2Potato3Potato
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for (var count = 4 ; count > 0 ; count-- ){ println(count);}
println(“Done”);
Count-controlled Loop
OUTPUT: 4321Done
Count Control Loop Example
Display integers and their squares from 1 through 10.
for (var i = 1; i <= 10; i++) { println(i + " " + i*i);}
For example
Display even integers and their squares from 1 through 10.
for (var i = 2; i <= 10; i = i+2) { println(i + " " + i*i);}
For example
Display integers and their squares from 10 down to 1.
for (var i = 10; i >= 1; i--) {println(i + " " + i*i);}
For example
Find square roots of 1.1, 1.2, 1.3, ..., 2.0
for (var x = 1.1; x <= 2.0; x =x+0.1) { println(x + " " + sqrt(x));}
Compute and return n! = 1 2 3 ... n.
var product = 1; for (var i = 2; i <= n; i++) {
product = product * i;}
For example
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