Just started c++ today, weird issue

[newbjohn]

Hi, just registered. this is day 1 of my c++ career, so this is going to be extremely basic.

My program is supposed to do two things, 1) count and display how many negative numbers the user enters, 2) use a cin at the end to prevent the command prompt window from closing before I can read the amount. The cin the best way I know how to create a pause just before the program ends.

For some reason, it won't pause for input.
I'm using dev-c++ IDE

#include <iostream>
int main()
{
int var = 0, count = 0, thiscoutwilloutput = 0, thiscinwontletuserinput;
while(std::cin >> var){
if (var < 0){
count ++;
}
}
std::cout << count << std::endl;
std::cout << thiscoutwilloutput;
std::cin >> thiscinwontletuserinput;
return 0;
}

thanks in advance.

[Danny]

The problem is here:
while(std::cin >> var){

This expression doesn't do what you expect it to. It's better to read
cin>>var first and then check its value:
while (var)
{
//..
}

[newbjohn]

Really?

Tragic news, since one of my books, C++ Primer, will be using this method.

I'm shocked that a technique used as early as page 26 of a very popular book won't be applicable : /

Maybe I'll try a different compiler.

edit by admin: you may not advertise on this forum, thank you

[jonnin]

its just at typical while loop logic issue.
you cant say

while(whatever)
{
read(whatever)
}

because whatever needs an initial value so you can enter the loop that first time. So you either hard code to enter one time (int whatever = 1) or you read it first (do / while)

[Danny]

Really?

Tragic news, since one of my books, C++ Primer, will be using this method.

I'm shocked that a technique used as early as page 26 of a very popular book won't be applicable : /

Maybe I'll try a different compiler.



You've solved a mystery for me. I have seen quite a few posts that use this incorrect idiom and wondered where they all came from. Anyway, that book should be fixed or possible replaced with a better C++ book (and there are plenty of those, fortunately).

[newbjohn]

edit by admin: you may not advertise on this forum, thank you

you're mistaken..


You've solved a mystery for me. I have seen quite a few posts that use this incorrect idiom and wondered where they all came from. Anyway, that book should be fixed or possible replaced with a better C++ book (and there are plenty of those, fortunately).


What a shocker, I found this book to be well praised when I was researching my purchase. Good thing this (http://www.amazon.com/C%2B%2B-Dummies-Stephen-Randy-Davis/dp/0764568523/ref=sr_1_1/102-7721036-0082548?ie=UTF8&s=books&qid=1181017584&sr=8-1) is shipping atm, even if its not as intelligent and thorough I suppose it could be more standard.

This (http://www.parashift.com/c++-faq-lite/input-output.html#faq-15.2)seems to be touching on what I'm experiencing.

[JPnyc]

That's entirely possible. However, a direct link to a book for sale on amazon will be taken as advertising roughly 100% of the time, whether correct or not.

[Danny]

Personally, I wouldn't recommend books for dummies, particularly not when C++ is concerned. I can recommend many other C++ books which are known to be accurate, clear and up-to date. C++ Primer by Lippman et al. is very good.
The C++ Programming Language by Stroustrup is still one of the best C++ books around although it's a bit over the top for a beginner.

[newbjohn]

Odd thing is after reading the edit, I first thought it looked like I was advertising via a smear campaign against the compiler, as if I contrived the question to prompt a "try this compiler" response. I thought this book would be common amongst many crowds, so much so that I linked to it to clarify that I did have the most recent version. The link was just what google returned. I know I don't have to explain myself, I just want to tell the story of what happened.

Anyhow, perhaps I'll only link to products that I do indeed know are popular.. in which case a link to it on amazon wouldn't be taken as an ad.


edit:
sorry for yet another edit, I'm just a bit out of my element right now.

Personally, I wouldn't recommend books for dummies, particularly not when C++ is concerned. I can recommend many other C++ books which are known to be accurate, clear and up-to date. C++ Primer by Lippman et al. is very good.
The C++ Programming Language by Stroustrup is still one of the best C++ books around although it's a bit over the top for a beginner.

Ok thanks. I got the dummies book in case I hid a barrier in the primer. Looking forward to Stroustrup's someday :)