Changing function based on a condition?

[LogicWavelength]

I was wondering if it's possible to have ONE function perform a different task, depending on some condition, or would I have to make separate functions? Here's my example:

		int x, y, z, product;

		x = getData();
		y = getData();
		z = getData();

int getData()
{
	int num;
	cout	<< "Please enter a number: ";
	cin	>> num;
	return num;
}

That was an in-class exercise. BUT... can I have getData say something like "Please enter first number: " then "Please enter second number: ", etc? ... or would I need three separate functions saying three separate things? I am working on a different project, and if I can do this, it would be great! So... is there a way? I don't know enough yet to figure that out. By the way... just pointing me in the right direction is fine... I don't want to have the answer handed over - I want to learn how myself. Also, we haven't learned pointers or any of that stuff yet... just doing functions now.

[VictorN]

I was wondering if it's possible to have ONE function perform a different task, depending on some condition, or would I have to make separate functions?

Yes, it is possible.
Whether you "have to make separate functions" or not as usual depends...

[Lindley]

Generally speaking, this is what function parameters are for.

[DivyaG12]

Yes, you can use the same function..pass parameters with the help of the function getdata() you are calling..hope this helps!!

[LogicWavelength]

...so I can use a placeholder variable as a parameter to send the function different info... then based on the parameter, use an if statement to make the function cout something new?

int x, y, z, product, variable;

                variable = 0;
		x = getData(variable);
                variable = 1;
		y = getData(variable);
                variable = 2;
		z = getData(variable);

int getData()
{
	int num;
	if (variable = 0)
        {
        cout	<< "Please enter the first number: ";
	cin	>> num;
        }
        else if.... etc, etc, etc.
	return num;
}

[Paul McKenzie]

...so I can use a placeholder variable as a parameter to send the function different info... then based on the parameter, use an if statement to make the function cout something new?

Just try it and see:

#include <iostream>

using namespace std;

int getData(int nWhichData)
{
   const char* varName = "xyz";
   cout << "Please enter value for " << varName[nWhichData] << " : " ;
   int value;
   cin >> value;
   return value;
}

int main()
{
   int x, y, z;
   x = getData(0);   
   y = getData(1);   
   z = getData(2);   
}

Regards,

Paul McKenzie

[LogicWavelength]

Thanks Paul! That's actually over my head with some of the code you wrote... I actually got back to my computer and tried what I wrote before - and it worked... minus the assignment error I had in my function. I'm sure yours would work too... but if I handed in something that had that in there my professor would know I didn't do it! Can't wait until I understand what you wrote there.

[Lindley]

You should be covering arrays soon if you haven't already.

[nuzzle]

...so I can use a placeholder variable as a parameter to send the function different info... then based on the parameter, use an if statement to make the function cout something new?

... or you can send the prompt string as a parameter to the input function.

How you generalize a function by the use of parameters may differ. The lesson is that parametrisation is one major way of making code more abstract in order to make it more general. Isolate what differs and make it a parameter.

[LogicWavelength]

You should be covering arrays soon if you haven't already.

We actually did arrays first... I just don't understand what you mean or how that applies to this problem.... I didn't get the varName[nWhichData] part he wrote. I have a lot to learn, I know.

[Lindley]

Well then, which part is unclear?

[monarch_dodra]

Maybe its clearer like this?

#include <iostream>

using namespace std;

int getData(int nWhichData)
{
   const char varName[4] = "xyz";
   cout << "Please enter value for " << varName[nWhichData] << " : " ;
   int value;
   cin >> value;
   return value;
}

int main()
{
   int x, y, z;
   x = getData(0);   
   y = getData(1);   
   z = getData(2);   
}

This uses array semantics rather than pointer semantics. It is morally equivalent. There are subtle differences between the two, but nothing you need to worry about.

[LogicWavelength]

ummm... yea that part. I don't understand how that array solution really works. I mean, I see what it does, but I'd never have thought of that. Here's some snippets from my actual (now, finished) project:

		//--GETTING DATA FROM USER--//
		int foo = 0;
		studio = getData(foo);
		foo = 1;
		oneBed = getData(foo);
		foo = 2;
		twoBed = getData(foo);

and here is the function definition:

int getData(int foo)
{
	int num;
	if (foo == 0)
	{
		cout	<< "How many studio apartments?: ";
		cin		>> num;
	}
	else if (foo == 1)
	{
		cout	<< "How many one-bedroom apartments?: ";
		cin		>> num;
	}
	else if (foo == 2)
	{
		cout	<< "How many two-bedroom apartments?: ";
		cin		>> num;
	}

	return num;
}

EDIT: On a umpteenth look at it, I see that you are using the array to send the 0, 1, 2 to the function parameter rather than manually assigning it like I did... correct? ...and that would allow the program to call those specific actions of the function later if needed, whereas my foo is now stuck assigned to 2... correct?

[Lindley]

		//--GETTING DATA FROM USER--//
		int foo = 0;
		studio = getData(foo);
		foo = 1;
		oneBed = getData(foo);
		foo = 2;
		twoBed = getData(foo);

There's no need to assign a value to a variable just to pass it. Since the function is making a copy of its argument anyway (pass-by-value), you can just pass the constant directly. So this is equivalent to:

                //--GETTING DATA FROM USER--//
		studio = getData(0);
		oneBed = getData(1);
		twoBed = getData(2);

regardless of what's in getData() (and assuming you don't need the fact that foo == 2 later in the main function of course).

int getData(int foo)
{
	int num;
	if (foo == 0)
	{
		cout	<< "How many studio apartments?: ";
		cin		>> num;
	}
	else if (foo == 1)
	{
		cout	<< "How many one-bedroom apartments?: ";
		cin		>> num;
	}
	else if (foo == 2)
	{
		cout	<< "How many two-bedroom apartments?: ";
		cin		>> num;
	}

	return num;
}

We can use an array in place of your if/else structure here, because the only difference between the three conditions is the type of apartment, and because your valid foo values are conveniently array-friendly anyway. This is simply a matter of condensing code, it doesn't change the behavior at all:

int getData(int foo)
{
        const std::string apttypes[3] = {"studio", "one-bedroom", "two-bedroom"};
        int num;
        assert(foo >= 0 && foo < 3);
        cout << "How many " << apttype[foo] << " apartments?: ";
        cin >> num;
        return num;
}

I added the assert() to catch any invalid parameters. Note this check is only done when debugging; an optimized build will omit it (that's how assert works).

We could have made apttype an array of const char*s rather than std::strings, it wouldn't make a difference in this case.

[LogicWavelength]

I just realized, by looking at your examples, that my function call was over-complicated. Here is a better version. Sorry for the noob-ness.

		//--GETTING DATA FROM USER--//
		studio = getData(0);
		oneBed = getData(1);
		twoBed = getData(2);

EDIT: I posted that without seeing your response, Lindley! Haha...