Function that calculates the arithmetic mean using vectors?

[Protoman]

I have a function that calculates the mean of the some numbers; I need
it to accept any number of parameters (one needs to be the number of
the other parameters) Can you help me out here? Here's the function:

const long double& mean(long long x)
{
vector<int> v(x);
for(int i= 1; i <=x; ++i)
{
v.push_back(i);
}
const long double ret=accumulate( v.begin(), v.end(), 0.0) / v.size();
return ret;
}

I want it to calculate the vector size at runtime. If you could help me
out, that'd be great. Thanks!!!

[Protoman]

OK, how do I test if my variables, num and temp, are characters, like a
or b? I need to make my code idiot proof.

[John Harrison]

Protoman wrote:

OK, how do I test if my variables, num and temp, are characters, like a
or b? I need to make my code idiot proof.

This question gets asked a lot. If you search the archive you'll get
lots of answers.

The only perfectly idiot proof method is to read a line into string,
check the string is in the correct form, and then convert to a number.

For a very nearly as good method see the 'resurrecting cin' thread by
float_dublin (c.l.c++ only). The full method doesn't come out until the
end so be prepared to read some less than complete posts (including one
by me).

john

[John Harrison]

John Harrison wrote:

Protoman wrote:

OK, how do I test if my variables, num and temp, are characters, like a
or b? I need to make my code idiot proof.

This question gets asked a lot. If you search the archive you'll get
lots of answers.

The only perfectly idiot proof method is to read a line into string,
check the string is in the correct form, and then convert to a number.

For a very nearly as good method see the 'resurrecting cin' thread by
float_dublin (c.l.c++ only). The full method doesn't come out until the
end so be prepared to read some less than complete posts (including one
by me).

john

For a bonus point, see if you can work out what the incorrect input is
that the 'resurrecting cin' method will accept, but the perfect method
will reject.

john

[Protoman]

OK, here's the idiot proof input funct:

template<class T>
void input(vector<T> & v)
{
cout << "Enter the number of items: " << endl;
int num;
cin >> num;
if(num==0)
abort();
else if(!cin)
abort();
else
for(int i=0;i<num;++i)
{
cout << "Enter a number: ";
T temp;
cin >> temp;
if(!cin)
abort();
else
v.push_back(tem p);
}
}

Any other suggestions for me?

[John Harrison]

Protoman wrote:

OK, here's the idiot proof input funct:

template<class T>
void input(vector<T> & v)
{
cout << "Enter the number of items: " << endl;
int num;
cin >> num;
if(num==0)
abort();
else if(!cin)
abort();
else
for(int i=0;i<num;++i)
{
cout << "Enter a number: ";
T temp;
cin >> temp;
if(!cin)
abort();
else
v.push_back(tem p);
}
}

Any other suggestions for me?

It works, but the idiots aren't going to be very happy when the program
aborts. I would have suggested some sort of error recovery, 'Hey idiot!
Please enter the number again', that kind of thing.

john

[BobR]

Protoman wrote in message
<11************ **********@g14g 2000cwa.googleg roups.com>...

Oh, and I think there's a function in cstdlib that terminates the
program; could you tell me what that function is?

If you can read this NG, you can read the docs for stdlib. <G>

You are thinking of 'exit()', BUT, don't use that for normal program
termination. It's intended as an 'emergency exit' (it's possible to shoot
yourself in the foot - or worse!).
All you need to do in your 'for(;;)' loop is execute 'break;', like you are
doing, and the 'main()' will finish, terminating your program normally.
You might find 'while(conditio n){}' a little cleaner/clearer than 'for(;;)'
(like Mr. Huber showed you.).

For your error checking question; look up 'isalpha' and 'isdigit' for an
idea.

What book are you using?

You might find this site interesting.
www.BruceEckel.com -> Books -> "Thinking in C++, vol. 1"
(since it only costs $(a download))
Two heads are better than one, and so are two books!

alt.comp.lang.l earn.c-c++ faq:
http://www.comeaucomputing.com/learn/faq/

Hope that helps. Good luck.
--
Bob R
POVrookie
--
MinGW (GNU compiler): http://www.mingw.org/
Dev-C++ IDE: http://www.bloodshed.net/
POVray: http://www.povray.org/

[Protoman]

OK here's the input function that doesn't abort on bad data:

template<class T>
void input(vector<T> & v)
{
start:
cout << "Enter the number of items: " << endl;
int num;
cin >> num;
if(num==0)
{
cout << "Try again, with a number this time ";
goto start;
}
else if(!cin)
{
cout << "Try again, with a number this time ";
goto start;
}
else
for(int i=0;i<num;++i)
{
start2:
cout << "Enter a number: ";
T temp;
cin >> temp;
if(!cin)
{
cout << "Try again, with a number this time ";
goto start2;
}
else
v.push_back(tem p);
}
}

But it keeps displaying the same message over and over again; what's
wrong? Thanks for the help!!! BTW, I use Learn C++ in 21 Days and
Standard C++ Bible. And my teacher told me there's a book that tells
you everything you can and can't do in C++. Could you tell me the name
of that book please? Thanks!!!

[John Harrison]

Protoman wrote:

OK here's the input function that doesn't abort on bad data:

template<class T>
void input(vector<T> & v)
{
start:
cout << "Enter the number of items: " << endl;
int num;
cin >> num;
if(num==0)
{
cout << "Try again, with a number this time ";
goto start;
}
else if(!cin)
{
cout << "Try again, with a number this time ";
goto start;
}
else
for(int i=0;i<num;++i)
{
start2:
cout << "Enter a number: ";
T temp;
cin >> temp;
if(!cin)
{
cout << "Try again, with a number this time ";
goto start2;
}
else
v.push_back(tem p);
}
}

But it keeps displaying the same message over and over again; what's
wrong? Thanks for the help!!! BTW, I use Learn C++ in 21 Days and
Standard C++ Bible. And my teacher told me there's a book that tells
you everything you can and can't do in C++. Could you tell me the name
of that book please? Thanks!!!

There is nothing that cannot be done in C++, it is a general purpose
language. Of course there are somethings that are easy to do and some
that are difficult, compared to other languages.

As already advised read the thread 'resurrecting cin' on c.l.c++. It is
about exactly this topic. If you what to research this issue see if your
books say something about iostreams and error state.

Try and develop the skills to research answers to your own questions, at
the moment you want to be spoon fed.

john

[Protoman]

No, that book I was talking about, it tells you what the syntax
permits, not the language itself. I'm just going to print an error
message, then abort. Saves me the trouble. And what would "COBOL style
C++" look like?

[John Harrison]

Protoman wrote:

No, that book I was talking about, it tells you what the syntax
permits, not the language itself. I'm just going to print an error
message, then abort. Saves me the trouble. And what would "COBOL style
C++" look like?

I have no idea.

john