For Loops3:15 with Jeremy McLain
Some while loops can be written more succinctly as for loops.
This pattern of using an integer that increases each time the loop runs, is so 0:00 common that there's a special kind of loop just for that. 0:04 It's called a for loop. 0:08 I'll write what that looks like lower existing loops so we can compare the two. 0:10 This is doing 0:15 exactly the same 0:22 thing the while loop, up here does. 0:32 We can break our while loop up here into for parts. 0:38 First, we declare index as an integer and initialize it to 0. 0:41 Second, we check to see if we’ve looped through all the indexes of the array. 0:46 Third, we do something with each of the array items Fourth, we increment index so 0:51 that the next time through the loop we're getting the next item in the array. 0:57 For loops also have the same for parts only there written more concisely. 1:03 Here's where we declare index as an integer and initialize it to zero. 1:09 Here's where we check to see if we've loop through all the indexes of the array. 1:13 The body of the loop is used for doing something with the array item. 1:18 And here's where we increment index so 1:22 that the next time through the loop we're getting the next item in the array. 1:25 Just think of for loops as condensed while loops. 1:30 Now that we have this for loop we don't need this while loop anymore. 1:34 For loops aren't only used for looping through a race. 1:39 They're also really handy when we want to count from one number to another. 1:42 We can set the starting number here and it can be any number we want. 1:47 We decide where to stop counting here. 1:52 This can be any condition that eventually stops the loop by evaluating to false. 1:55 Each time the loop runs, index will count up by one. 2:00 In fact, this variable is often called a loop counter. 2:05 We could also count by more than one by using plus equals like this. 2:09 This will count up by two. 2:14 We want to count by one so I'll change this back to index plus plus. 2:17 Because this variable index is being declared right here, 2:22 its scope is limited to inside of the loop. 2:26 That means that it can only be used inside the 4 loop. 2:30 If we want to access the loop counter variable after the 4 loop has ended, 2:34 we'd have to move the declaration up here above the 4 loop somewhere. 2:38 [PAUSE] It may look strange, but this is perfectly valid code. 2:42 When reading code, you'll notice that most for loops use the single letter I 2:52 as the name of the loop counter variable. 2:57 This tradition goes all the way back to the first programming languages created. 3:00 You can name it whatever makes sense for your code though. 3:05 Just to maintain tradition I'll shorten index to I for us. 3:08
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