Question about passing & receiving parameters

Guys,

I have a question or two about the following code segment that I hope someone will answer. This was part of a source code file provided on the CD, so I did not pick the variables.

Code:

---

void output(float a)
{
    printf("The average is %.2f\n", a);
}

int main()
{
    int    num1, num2, num3;
    float  ave;

    num1 = input(1);
    num2 = input(2);
    num3 = input(3);

    ave = average3(num1, num2, num3);

    output(ave);
}

---

My questions:

1) When passing ave to output as 'a' why don't we have to declare 'float a;' in the function--or are we in essence doing that when we declare the function?

2) I have seen a couple different examples of parameters that should be included in the main(). In a case like this, what would be the recommended parameter(s) to include for main to receive? ...void?

The texts I have don't seem to agree and I have no one else to ask; so I very much appreciate the help.

TB

Quote:

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2) I have seen a couple different examples of parameters that should be included in the main(). In a case like this, what would be the recommended parameter(s) to include for main to receive? ...void?

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In C and C++, main(void) is the same as main(). In C, a parameter like func() is different from func(void) (but not in C++); the first means "parameters unknown" and the second "no parameters". So for a declaration, you can use either, but for a prototype you should use (void).

You may also have seen

Code:

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int main(int argc, char *argv[])

---

which accepts command line parameters. You don't need to use this.

There's an FAQ on the subject. [edit]http://faq.cprogramming.com/cgi-bin/...&id=1043284376[/edit]

Quote:

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1) When passing ave to output as 'a' why don't we have to declare 'float a;' in the function--or are we in essence doing that when we declare the function?

---

You're passing a float value to output(), which can call that float whatever it wants.

It's like this:

Code:

---

float a = 5;
float b = a;

---

It doesn't matter what b is called. It still gets the value of a.

Quote:

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1) When passing ave to output as 'a' why don't we have to declare 'float a;' in the function--or are we in essence doing that when we declare the function?

---

Yes the formal parameters gets declared for you so you don't need to bother with doing that in the function body.

Quote:

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Originally Posted by dwks

You're passing a float value to output(), which can call that float whatever it wants.

---

Ok...so passing a value to a function basically negates the need to declare any such variable in that receiving function--even though that might be the first use of 'a' or whatever else you tell it to receive?

Quote:

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Originally Posted by dwks

It's like this:

Code:

---

float a = 5;
float b = a;

---

It doesn't matter what b is called. It still gets the value of a.

---

But it *does* matter what 'b' is called--you need to assign the value of 'a' to something. When you declared 'b' it was created, so now it's available for assignment; same as if you had named it 'bb' or 'bbb' or...

I guess what I am trying to say is that I completely understand about declaring & initializing variables--and making assignments to them. But I guess I just didn't understand whether or not there is a difference between passing a value (and not having to declare it in the new function), and declaring it in the first place.

So from the code sample above if I pass 'ave' to output(), the only way that the new function will know anything about the parameter is by me telling it to expect a float variable; and then passing by value into it. Do I have that straight?

I will read that faq that dwks linked--though I think I might have already.

Thanks for the help.

TB

Quote:

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Originally Posted by OnionKnight

Yes the formal parameters gets declared for you so you don't need to bother with doing that in the function body.

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Thanks OnionKnight...

I was responding to another post when you posted. That clarified it for me.

TB

Quote:

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So from the code sample above if I pass 'ave' to output(), the only way that the new function will know anything about the parameter is by me telling it to expect a float variable; and then passing by value into it. Do I have that straight?

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Exactly. The new function doesn't know, and doesn't care, what the original variable was called.

Quote:

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Originally Posted by dwks

Exactly. The new function doesn't know, and doesn't care, what the original variable was called.

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Thanks.

And thanks for the link--I had NOT seen it, and appreciate it very much.

TB

On a side note and for future reference you will do yourself a good favor if you make your prototype in a header exactly match the function definition in the module file.

Header

Code:

---

float Add(float v1,float v2);

---

Module

Code:

---

float Add(float v1,float v2)
{
  return v1+v2;
}

---

Technically it does NOT have to be this way and will compile using different parameter names, however, I do not think it is a good practice.

Bubba,

Good tip...

I just learned about function prototypes last week. I guess I knew about them for quite some time, but didn't know what they really were. But I can see how they would really be a useful tool--especially down the road a bit.

TB