WEBVTT 00:00.200 --> 00:02.660 Next we have the for loop. 00:02.690 --> 00:05.090 This one is quite flexible. 00:05.120 --> 00:12.020 It exists in different programming languages, so if you've ever programmed in any language, you should 00:12.020 --> 00:14.780 be pretty familiar with the for loop. 00:14.810 --> 00:16.730 Anyway, let's go through it. 00:16.760 --> 00:25.040 Now this one is actually quite flexible, yet often it's used to do a simple operation like repeat something 00:25.070 --> 00:27.290 5 or 10 times. 00:27.320 --> 00:33.530 So it has the most complex syntax actually from all the other loops. 00:33.530 --> 00:35.180 And let's go through it. 00:35.180 --> 00:37.250 So it starts with the for keyword. 00:37.250 --> 00:41.000 And there are actually three expressions inside. 00:41.000 --> 00:50.540 So there is this first expression that is always run once only once at the beginning of the loop. 00:50.870 --> 00:57.050 This is often used to initialize the variable that counts the number. 00:57.050 --> 01:00.020 If you are just trying to do something five times. 01:00.020 --> 01:01.730 We're gonna see that in a second. 01:01.820 --> 01:06.500 And the next step is always to evaluate the condition. 01:06.530 --> 01:09.050 That's the second expression. 01:09.050 --> 01:17.660 And if this condition is true, then we just execute the body of the for loop, which is some statements 01:17.660 --> 01:19.550 or no statements. 01:19.910 --> 01:27.620 If this condition is false, we immediately well basically we are done executing the loop. 01:27.650 --> 01:30.440 But there is one more expression. 01:30.440 --> 01:41.060 So if the condition was true and statements were executed, then we unconditionally run this third expression. 01:41.060 --> 01:43.190 And this happens all the time. 01:43.190 --> 01:51.620 So this third expression is always run after the statements in the for loop body are executed. 01:51.620 --> 01:57.930 And then we go back to the condition to the second expression to see if it's still true. 01:57.930 --> 02:05.850 And again, we decide if we should run the body of the for loop again, or just be done with the loop 02:05.850 --> 02:06.660 already. 02:06.870 --> 02:10.320 Now let's see that in our real example. 02:11.850 --> 02:15.420 So let's start by creating a file for our exercise. 02:15.420 --> 02:17.400 Let's call it for PHP. 02:18.960 --> 02:21.540 And let's get started with the PHP tag. 02:21.540 --> 02:24.990 What I'm going to do here is a rocket launch countdown. 02:24.990 --> 02:27.870 So a funny little exercise. 02:27.870 --> 02:37.860 So first we're going to echo the rocket launch countdown so people know what they are waiting for. 02:37.980 --> 02:41.190 And then let's define the for loop. 02:41.190 --> 02:48.660 As usual with all those control structures we've got parentheses right after the keyword. 02:48.660 --> 02:51.750 And now I set about three expressions. 02:51.750 --> 02:55.470 So the first one runs only once. 02:55.470 --> 03:02.670 Ones, so it's often used to initialize a variable that will be used to control this loop. 03:03.000 --> 03:06.540 So we can initialize it with ten. 03:06.540 --> 03:09.480 So this here is defining a variable. 03:09.510 --> 03:10.290 Keep in mind. 03:10.320 --> 03:14.460 This variable is not available outside this for loop. 03:15.030 --> 03:18.150 We're going to talk about that more later on. 03:18.180 --> 03:20.850 And then we've got a condition. 03:20.850 --> 03:25.710 So this is the condition that will be run every single time to. 03:25.740 --> 03:30.270 Determine if the body of this for loop should be run or not. 03:30.300 --> 03:34.830 So this is this E which is also. 03:34.860 --> 03:38.820 Often the name of the variable used in the for loop. 03:38.820 --> 03:40.500 That's just a convention. 03:41.460 --> 03:42.870 If it's more than. 03:42.900 --> 03:45.090 Zero then we should continue. 03:45.090 --> 03:53.430 And this third expression is something that is always run after the body of. 03:53.460 --> 03:55.510 This loop is executed. 03:55.510 --> 03:59.770 So can you think what this should be? 04:00.430 --> 04:05.740 What would make all this here actually make sense? 04:05.770 --> 04:11.740 Well, this is decreasing this I variable value by one. 04:11.740 --> 04:19.600 So to decrease the value of a variable by one, you can use this minus minus operator on the variable 04:19.600 --> 04:22.900 which will just decrease the value by one. 04:23.350 --> 04:31.060 Next we've got the curly braces which would be optional if you would only have one statement inside 04:31.060 --> 04:32.800 this for loop body. 04:32.800 --> 04:34.690 But we're going to have more. 04:35.260 --> 04:42.430 So the first thing inside is to just say what's the current counter value. 04:42.640 --> 04:48.970 So let's concatenate that with three dots like this. 04:48.970 --> 04:56.020 And we need to check if maybe it's the lift of time. 04:56.410 --> 05:01.840 So we're going to use the if statement and we're going to verify if one equals I. 05:02.110 --> 05:10.300 That's another thing you might keep in mind in comparisons that you add to if statements or any other 05:10.300 --> 05:11.440 control structures. 05:11.440 --> 05:21.220 So basically the conditions that you create that it is always safer to compare a value on the left to 05:21.250 --> 05:22.840 the variable on the right. 05:22.840 --> 05:23.860 Why? 05:23.890 --> 05:27.670 Well, because if you would do it the other way. 05:30.040 --> 05:33.550 You might forget one equality sign. 05:33.550 --> 05:37.720 And this here is a completely different statement. 05:37.720 --> 05:42.400 This is assigning one to this variable every single time. 05:42.400 --> 05:47.290 And trust me that this just happens all the time, even to the experienced engineers. 05:47.290 --> 05:50.620 And you can't assign anything to a value. 05:50.620 --> 05:58.810 and this would immediately throw an error if you would accidentally use this assignment instead of comparison. 05:59.020 --> 06:04.720 Okay, so when this is true, we just say that it's the liftoff time. 06:06.070 --> 06:09.580 Let's add some funny symbol. 06:12.580 --> 06:16.330 Okay, let be a rocket and a new line. 06:18.550 --> 06:22.240 And then let's just sleep for one second. 06:22.240 --> 06:26.350 So we have some delay between all those messages showing up. 06:26.380 --> 06:28.720 Okay, we are ready to try this out. 06:29.650 --> 06:33.760 So now in the terminal just type PHP four dot PHP. 06:33.790 --> 06:34.570 There we have it. 06:34.600 --> 06:36.430 The countdown is happening. 06:40.060 --> 06:41.050 Almost there. 06:41.050 --> 06:43.900 And there is the liftoff. 06:43.900 --> 06:46.090 And the program has finished. 06:46.420 --> 06:52.680 So if I would be to summarize the for loop and maybe how it differs from the while loop. 06:53.160 --> 06:59.310 There are some obvious differences, but we can also say that those loops are pretty similar. 06:59.310 --> 07:00.570 They do the same thing. 07:00.600 --> 07:03.690 They let you execute some code a couple of times. 07:03.690 --> 07:07.170 So here there is just one expression, which is a condition. 07:07.170 --> 07:10.380 And the for loop is maybe more complex. 07:10.380 --> 07:16.470 And the use cases, well I think that this just feels more natural. 07:16.800 --> 07:23.190 Uh, given the case that you need to handle which of those loops to use. 07:23.190 --> 07:27.570 So I wouldn't go with any generic recommendations. 07:27.570 --> 07:28.890 There are many options. 07:28.890 --> 07:32.520 So we would be just choosing the best options. 07:32.520 --> 07:36.000 That just feels more natural for the job. 07:36.000 --> 07:45.270 But eventually to actually have this instincts of which loops you should be choosing, well, you just 07:45.270 --> 07:47.610 need to write a lot of code.