Passing on parameters

Can anyone tell me how to pass on parameters to a function?

Code:

void F(int a)
 
{
 
   a = 10;
 
}
 
 
 
int main(int argc, char* argv[])
 
{
 
  
 
   int a = 0;
F(a);
cout << a << endl;
}

a will 0, but not 10. And the book says that it has something to do with passing parameters.

you pass the parameter by value - it means any changes to vaariable inside the function are not visible outside.

If you want to see the changes - you need to pass it by reference

Code:

void f(int& val)
{
   val = 10;
}
int main()
{
   int a = 0;
   f(a);
   std::cout << a << std::endl;
   return 0;
}

or just return the result...

Oh, can you just explain to me how the parameters passed by value in the example? The book says that a copy of the parameter has been made. But I don't understand.

It is just like it says -

Code:

int f(int val)
{
   val = 10;
}
int main()
{
   int a = 0;
   f(a);
   return 0;
}

when main is started the automatic variable a is allocated on stack and its vaue is set to 0
when f is going to start another automatic varible - I even have given it different name - val is allocated on the stack
and the value of a is copied to this new location - it is called passing parameters by value.

all changes that f makes to this new variable do not affect in any way the original variable a.

So when f is finished - the value of a is left intact

oh. now I understand. Do you have any books on functions?

I suggest reading a good introductory book on C++, e.g., Accelerated C++.

But, is it good to read as many books as possible?

Originally Posted by Allen

But, is it good to read as many books as possible?

Yes, if they are good books, but trying to read them simultaneously will probably be problematic for you.