Calling a function

Posted on 2003-11-23
Last Modified: 2010-04-15
When I want to call a function. Do you have to send a parameter to it or can you just leave it blank.  It is void function so there will be nothing returned.  
Question by:buckeyes33
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LVL 24

Expert Comment

ID: 9806847
it depends on the declration of functions.

if the function is declared to have 2 parameter as input, it should be supplied 2 parameters.
void returning take care of what is expected to return back from function.

Expert Comment

ID: 9806854
It depends on the so-called parameter list of your function.
For example:
void foo(void);  //equivalent to void foo( ).
Call: foo();       //legal
       foo(someParam); //illegal. foo does not take any parameter.

void foo1(int x); //or any number of parameters.
Call: foo1(); //illegal.
       int a = 0;
       foo1(a); //legal.
       char ch = 'a';
       foo1(ch); //warning. usually type casting is required for parameters whose types don't match that specified in the
                     //parameter list.
       foo1(a, ch); //error. foo1 does not take 2 parameters.

So my advise is, look up the prototype of your function. What types of parameters does it take? And how many?

LVL 24

Expert Comment

ID: 9806857
void swap(double& x, double& y)
{                                                         /* exchange the values of x and y */
double temp = x;
x = y;
y = temp;

int main(){
 double a = 22.2, b = 44.4;

here function is void swap( para1, para2)

then here it need 2 input parameters and it will return nothing.
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Author Comment

ID: 9806868
I did not make much sense before.  
I calling function X.  function X is going to do all calculations needed and then print results.  This is without using the parameter that is would be sent to function X.

Is there a need to send a parameter to function X since it would not be needed.  

Accepted Solution

n_fortynine earned 125 total points
ID: 9806945
If your function does not NEED the parameter, but its prototype DEMANDS on, you'll still need to suplly one to it. Even a dummy one.

Another way is to make the function taking in default parameters:
For example:
void foo(int x);
Call: foo(); //error.
       int a = 0;
       foo(a); //OK.

void foo1(int x = 0);
Call: foo1(); //OK now that you don't supply one, if foo1 needs to use x, x will have a value set at 0.
       int a = 2;
       foo1(a); //OK. Now foo1 will use x = 2.

Expert Comment

ID: 9806949
should read... DEMANDS one.

Author Comment

ID: 9806978
ok thanks.

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