Can anyone tell me how to pass on parameters to a function?
Can anyone tell me how to pass on parameters to a function?
a will 0, but not 10. And the book says that it has something to do with passing parameters.Code:void F(int a) { a = 10; } int main(int argc, char* argv[]) { int a = 0; F(a); cout << a << endl; }
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
or just return the result...Code:void f(int& val) { val = 10; } int main() { int a = 0; f(a); std::cout << a << std::endl; return 0; }
All problems in computer science can be solved by another level of indirection,
except for the problem of too many layers of indirection.
– David J. Wheeler
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 -
when main is started the automatic variable a is allocated on stack and its vaue is set to 0Code:int f(int val) { val = 10; } int main() { int a = 0; f(a); return 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
All problems in computer science can be solved by another level of indirection,
except for the problem of too many layers of indirection.
– David J. Wheeler
oh. now I understand. Do you have any books on functions?
I suggest reading a good introductory book on C++, e.g., Accelerated C++.
Look up a C++ Reference and learn How To Ask Questions The Smart WayOriginally Posted by Bjarne Stroustrup (2000-10-14)
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.
Look up a C++ Reference and learn How To Ask Questions The Smart Way
