WEBVTT 00:00.860 --> 00:08.450 There are situations when you have one or more parameters that have values that are so frequently used 00:08.450 --> 00:14.210 that you want them to be treated as a default value for the parameter. 00:14.210 --> 00:20.600 So while still having the option of allowing the color to provide a different value if necessary. 00:20.600 --> 00:28.520 So to do this, you provide a default value in parameter parameter list of the definition here. 00:28.520 --> 00:31.040 So let's, let's make the void here. 00:31.040 --> 00:36.010 Make a new function named log message here. 00:36.020 --> 00:41.240 First is const string here message. 00:41.840 --> 00:44.420 Of course we have to include the string. 00:45.050 --> 00:45.740 Okay. 00:45.770 --> 00:47.030 Change string to. 00:47.210 --> 00:48.860 Yeah, we have to. 00:50.170 --> 00:51.250 Include. 00:51.520 --> 00:52.360 Include. 00:53.020 --> 00:54.190 String. 00:54.370 --> 00:55.150 Okay. 00:55.510 --> 00:56.650 And. 00:57.680 --> 00:58.780 We have to. 00:58.880 --> 01:01.340 Using namespace STD. 01:03.670 --> 01:05.110 Stayed here. 01:05.350 --> 01:14.680 And then we're going to create another bull here and bull clear screen. 01:15.860 --> 01:18.680 And we're going to equal to false here. 01:18.680 --> 01:26.330 As you can see, this is the first time we use the self initializing parameters in this course here. 01:26.330 --> 01:36.110 So and we're going to add the if the clear screen is true, then clear the clear the screen here, which 01:36.110 --> 01:37.670 we're going to write it here. 01:38.180 --> 01:39.170 Okay. 01:40.160 --> 01:42.050 Void, void. 01:42.050 --> 01:46.130 Clear the screen screen. 01:48.050 --> 01:48.320 Yeah. 01:50.030 --> 01:53.120 And we're going to call the clear the screen. 01:55.690 --> 02:01.580 Where the screen function here is the clear screen returns true. 02:01.600 --> 02:08.830 So in most cases, this function is expected to be used to print a single message, but occasionally 02:08.830 --> 02:12.140 the user may want to have the screen cleared first. 02:12.160 --> 02:17.760 Say for the first message or after a predetermined count of lines. 02:17.770 --> 02:26.260 So to accommodate this use of this function, the clear screen parameter is given the default value 02:26.260 --> 02:27.370 of false here. 02:27.370 --> 02:33.550 But the caller still has the option option of passing a value here. 02:33.550 --> 02:38.530 So now we're going to print the message here. 02:39.460 --> 02:39.920 Okay. 02:39.940 --> 02:45.610 Like this print message here and end the line. 02:45.610 --> 02:55.880 And in the main function, let's call this log message function here and write our message. 02:55.910 --> 02:58.640 First message here. 03:01.500 --> 03:04.290 And then we're going to pass the true here. 03:06.980 --> 03:09.920 And let's create another message here. 03:09.950 --> 03:12.920 This is the second message here. 03:13.220 --> 03:18.910 Without the, uh, without the second parameter bool parameter here. 03:18.920 --> 03:25.610 As you can see, if we made this differently, like if we delete this, as you can see, this message 03:25.610 --> 03:34.670 gives error because the compiler knows if we don't have the second parameter, then the bool clear screen 03:34.670 --> 03:39.260 has to be false and we're going to like abstract virtual. 03:39.260 --> 03:46.120 We're going to have the virtual seven second parameter if we call that like the real world applications 03:46.130 --> 03:46.340 here. 03:46.340 --> 03:46.970 So. 03:48.260 --> 03:52.190 Now here we're going to add another we're going to create a bool here. 03:52.210 --> 03:56.470 So we're going to pass the user's decision. 03:57.400 --> 03:59.200 And here. 04:00.760 --> 04:07.930 We're going to here for, for example, let's, let's make the user decision, uh, true. 04:07.930 --> 04:10.510 And we're going to the log message here. 04:10.540 --> 04:12.940 Log message that third. 04:16.820 --> 04:24.170 Third message here, and we're going to pass the user decision as the variable here. 04:24.560 --> 04:25.190 Let's. 04:25.190 --> 04:25.790 Okay. 04:26.030 --> 04:27.050 So. 04:28.390 --> 04:33.670 Notice that default values occur in the function, not in the function prototype here. 04:33.670 --> 04:42.640 So if the log message function is declared in a header file, the prototype here should be like like 04:42.640 --> 04:49.180 the extern here we're going to add the extern and without these braces here we just have to write the 04:49.180 --> 04:51.190 parameters of our function. 04:51.190 --> 04:57.070 So if we call this function with extern, as you can see here, we're going to get the error here, 04:57.070 --> 04:58.630 but let's delete it. 04:59.760 --> 05:00.080 Oops. 05:00.090 --> 05:01.890 Uh, what's the problem here? 05:02.280 --> 05:03.690 We have the. 05:05.160 --> 05:06.150 Clear the screen. 05:06.150 --> 05:06.300 Yeah. 05:06.300 --> 05:08.610 We have to make it. 05:09.490 --> 05:11.140 Under it here. 05:25.340 --> 05:25.560 Here. 05:25.560 --> 05:26.750 Are we going to comment this up? 05:26.750 --> 05:31.370 Because this is the the program of next lecture. 05:31.370 --> 05:39.410 And as you can see, the compiler showed the tells that we have the problem here and we're going to 05:39.410 --> 05:43.550 firstly undefined reference to clear the screen here. 05:43.550 --> 05:49.850 So now we just we are not we we're not going to using this function for now. 05:51.410 --> 05:52.700 And we're going to delete that. 05:52.700 --> 05:56.270 And as you can see, we show the message on it here. 05:56.270 --> 05:57.320 So. 05:58.390 --> 06:00.130 Let's delete this as well. 06:00.730 --> 06:01.780 Like this here. 06:01.780 --> 06:08.080 And as you can see here, the first message, second message and third message printed here. 06:08.080 --> 06:14.170 And as you can see, the second in the 10th line, we didn't enter the second parameter. 06:14.170 --> 06:20.200 That's why the second, if we don't enter the second parameter, the compiler expects us that the second 06:20.200 --> 06:22.540 parameter is false here. 06:22.540 --> 06:30.100 So if we don't enter the second parameter, the second parameter will be automatically taken as false 06:30.100 --> 06:30.610 here. 06:30.610 --> 06:40.180 So actually you can treat the each parameter with a default value as representing the separate overload 06:40.180 --> 06:41.320 of the function. 06:41.320 --> 06:52.180 So conceptually here the log message function should be treated as two functions as I said earlier. 06:52.180 --> 06:59.810 So if you did, if you define a log message function that has just a const string parameter here, then 06:59.810 --> 07:04.520 the compiler will not know whether to call the function or the version. 07:04.520 --> 07:10.070 The clear the screen is given a default value of false here.