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There are situations when you have one or more parameters that have values that are so frequently used

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that you want them to be treated as a default value for the parameter.

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So while still having the option of allowing the color to provide a different value if necessary.

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So to do this, you provide a default value in parameter parameter list of the definition here.

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So let's, let's make the void here.

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Make a new function named log message here.

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First is const string here message.

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Of course we have to include the string.

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Okay.

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Change string to.

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Yeah, we have to.

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Include.

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Include.

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String.

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Okay.

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And.

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We have to.

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Using namespace STD.

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Stayed here.

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And then we're going to create another bull here and bull clear screen.

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And we're going to equal to false here.

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As you can see, this is the first time we use the self initializing parameters in this course here.

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So and we're going to add the if the clear screen is true, then clear the clear the screen here, which

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we're going to write it here.

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Okay.

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Void, void.

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Clear the screen screen.

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Yeah.

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And we're going to call the clear the screen.

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Where the screen function here is the clear screen returns true.

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So in most cases, this function is expected to be used to print a single message, but occasionally

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the user may want to have the screen cleared first.

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Say for the first message or after a predetermined count of lines.

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So to accommodate this use of this function, the clear screen parameter is given the default value

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of false here.

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But the caller still has the option option of passing a value here.

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So now we're going to print the message here.

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Okay.

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Like this print message here and end the line.

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And in the main function, let's call this log message function here and write our message.

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First message here.

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And then we're going to pass the true here.

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And let's create another message here.

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This is the second message here.

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Without the, uh, without the second parameter bool parameter here.

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As you can see, if we made this differently, like if we delete this, as you can see, this message

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gives error because the compiler knows if we don't have the second parameter, then the bool clear screen

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has to be false and we're going to like abstract virtual.

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We're going to have the virtual seven second parameter if we call that like the real world applications

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here.

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So.

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Now here we're going to add another we're going to create a bool here.

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So we're going to pass the user's decision.

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And here.

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We're going to here for, for example, let's, let's make the user decision, uh, true.

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And we're going to the log message here.

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Log message that third.

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Third message here, and we're going to pass the user decision as the variable here.

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Let's.

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Okay.

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So.

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Notice that default values occur in the function, not in the function prototype here.

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So if the log message function is declared in a header file, the prototype here should be like like

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the extern here we're going to add the extern and without these braces here we just have to write the

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parameters of our function.

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So if we call this function with extern, as you can see here, we're going to get the error here,

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but let's delete it.

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Oops.

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Uh, what's the problem here?

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We have the.

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Clear the screen.

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Yeah.

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We have to make it.

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Under it here.

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Here.

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Are we going to comment this up?

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Because this is the the program of next lecture.

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And as you can see, the compiler showed the tells that we have the problem here and we're going to

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firstly undefined reference to clear the screen here.

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So now we just we are not we we're not going to using this function for now.

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And we're going to delete that.

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And as you can see, we show the message on it here.

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So.

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Let's delete this as well.

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Like this here.

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And as you can see here, the first message, second message and third message printed here.

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And as you can see, the second in the 10th line, we didn't enter the second parameter.

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That's why the second, if we don't enter the second parameter, the compiler expects us that the second

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parameter is false here.

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So if we don't enter the second parameter, the second parameter will be automatically taken as false

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here.

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So actually you can treat the each parameter with a default value as representing the separate overload

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of the function.

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So conceptually here the log message function should be treated as two functions as I said earlier.

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So if you did, if you define a log message function that has just a const string parameter here, then

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the compiler will not know whether to call the function or the version.

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The clear the screen is given a default value of false here.