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Looping
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John Nunemaker
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September 24, 2009
Programming
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Looping
John Nunemaker
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September 24, 2009
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Transcript
loops executing code over and over again Thursday, September 24,
2009
Thursday, September 24, 2009
for loop loop a specified number of times; the only
loop you need to know http://www.w3schools.com/jS/js_loop_for.asp Thursday, September 24, 2009
for (var i=0; i < 5; i++) { // some
code to run } Thursday, September 24, 2009
for (var i=0; i < 5; i++) { // some
code to run } before any loops Thursday, September 24, 2009
for (var i=0; i < 5; i++) { // some
code to run } before each loop Thursday, September 24, 2009
for (var i=0; i < 5; i++) { // some
code to run } after each loop Thursday, September 24, 2009
for (var i=0; 0 < 5; i++) { // i
would be 0 } Thursday, September 24, 2009
for (var i=0; 1 < 5; i++) { // i
would be 1 } Thursday, September 24, 2009
for (var i=0; 2 < 5; i++) { // i
would be 2 } Thursday, September 24, 2009
for (var i=0; 3 < 5; i++) { // i
would be 3 } Thursday, September 24, 2009
for (var i=0; 4 < 5; i++) { // i
would be 4 } Thursday, September 24, 2009
for (var i=0; 5 < 5; i++) { // condition
false so this // would never happen } Thursday, September 24, 2009
for (var i=0; 5 < 5; i++) { // condition
false so this // would never happen } Thursday, September 24, 2009
var colors = ['red', 'green', 'blue']; for(var i=0; i <
colors.length; i++) { colors[i]; } Thursday, September 24, 2009
var colors = ['red', 'green', 'blue']; for(var i=0, length=colors.length; i
< length; i++) { colors[i]; } Thursday, September 24, 2009
var colors = ['red', 'green', 'blue']; var length = colors.length;
for(var i=0; i < length; i++) { colors[i]; } Thursday, September 24, 2009
while loop loop while a condition is true http://www.w3schools.com/JS/js_loop_while.asp Thursday,
September 24, 2009
var i = 0; while (i < 5) { //
some code to run i++; } Thursday, September 24, 2009
var i = 0; while (i < 5) { //
some code to run i++; } before each loop Thursday, September 24, 2009
var i = 0; while (0 < 5) { //
i would be 0 i++; // i would be 1 } Thursday, September 24, 2009
var i = 0; while (1 < 5) { //
i would be 1 i++; // i would be 2 } Thursday, September 24, 2009
var i = 0; while (2 < 5) { //
i would be 2 i++; // i would be 3 } Thursday, September 24, 2009
var i = 0; while (3 < 5) { //
i would be 3 i++; // i would be 4 } Thursday, September 24, 2009
var i = 0; while (4 < 5) { //
i would be 4 i++; // i would be 5 } Thursday, September 24, 2009
var i = 0; while (5 < 5) { //
condition is false so // this would never happen i++; } Thursday, September 24, 2009
var i = 0; while (5 < 5) { //
condition is false so // this would never happen i++; } Thursday, September 24, 2009
for..in loop loop through the properties of an object http://www.w3schools.com/jS/js_loop_for_in.asp
Thursday, September 24, 2009
for (property in object) { // some code here }
Thursday, September 24, 2009
var person = { name: 'John Nunemaker', age: 27, married:
true, cat_owner: 'unfortunately' }; for (property in person) { property; person[property]; } Thursday, September 24, 2009
var person = { name: 'John Nunemaker', age: 27, married:
true, cat_owner: 'unfortunately' }; for (property in person) { property; // ‘name’ person[property]; // ‘John Nunemaker’ } Thursday, September 24, 2009
var person = { name: 'John Nunemaker', age: 27, married:
true, cat_owner: 'unfortunately' }; for (property in person) { property; // ‘age’ person[property]; // 27 } Thursday, September 24, 2009
var person = { name: 'John Nunemaker', age: 27, married:
true, cat_owner: 'unfortunately' }; for (property in person) { property; // ‘married’ person[property]; // true } Thursday, September 24, 2009
var person = { name: 'John Nunemaker', age: 27, married:
true, cat_owner: 'unfortunately' }; for (property in person) { property; // ‘cat_owner’ person[property]; // ‘unfortunately’ } Thursday, September 24, 2009
break break the current loop and continue with code after
loop if any http://www.w3schools.com/jS/js_break.asp Thursday, September 24, 2009
think “stop looping right now” Thursday, September 24, 2009
for (var i=0; i < 5; i++) { if (i
=== 2) { break; } i; } Thursday, September 24, 2009
for (var i=0; 0 < 5; i++) { if (0
=== 2) { // false break; } i; // 0 } Thursday, September 24, 2009
for (var i=0; 0 < 5; i++) { if (0
=== 2) { // false break; } i; // 0 } Thursday, September 24, 2009
for (var i=0; 1 < 5; i++) { if (1
=== 2) { // false break; } i; // 1 } Thursday, September 24, 2009
for (var i=0; 1 < 5; i++) { if (1
=== 2) { // false break; } i; // 1 } Thursday, September 24, 2009
for (var i=0; 2 < 5; i++) { if (2
=== 2) { // true break; // breaks out of loop } i; // never gets here } Thursday, September 24, 2009
for (var i=0; 2 < 5; i++) { if (2
=== 2) { // true break; // breaks out of loop } i; // never gets here } Thursday, September 24, 2009
most common use is switch statement, but good to know
it works elsewhere Thursday, September 24, 2009
continue break the current loop and continue with the next
value http://www.w3schools.com/jS/js_break.asp Thursday, September 24, 2009
think “skip current loop” Thursday, September 24, 2009
for (var i=0; i < 3; i++) { if (i
=== 1) { continue; } i; // comment } Thursday, September 24, 2009
for (var i=0; 0 < 3; i++) { if (0
=== 1) { // false continue; } i; // 0 } Thursday, September 24, 2009
for (var i=0; 0 < 3; i++) { if (0
=== 1) { // false continue; } i; // 0 } Thursday, September 24, 2009
for (var i=0; 1 < 3; i++) { if (1
=== 1) { // true continue; } i; // never gets here } Thursday, September 24, 2009
for (var i=0; 1 < 3; i++) { if (1
=== 1) { // true continue; } i; // never gets here } Thursday, September 24, 2009
for (var i=0; 2 < 3; i++) { if (2
=== 1) { // false continue; } i; // 2 } Thursday, September 24, 2009
for (var i=0; 2 < 3; i++) { if (2
=== 1) { // false continue; } i; // 2 } Thursday, September 24, 2009
for (var i=0; 3 < 3; i++) { // never
gets here if (i === 1) { continue; } i; } Thursday, September 24, 2009
for (var i=0; 3 < 3; i++) { // never
gets here if (i === 1) { continue; } i; } Thursday, September 24, 2009
assignment04 http://teaching.johnnunemaker.com/capp-30550/sessions/looping/ Thursday, September 24, 2009