Thread: C++ Cin Help!

Hello, I have a problem while CIN into an array of Chars.
Say If I declare an array of Chars of length 10 and prompt
the user for a CIN. How to I get the language to pick up only
say 5 letters?!?

Right now I have the CIN in a loop but it makes sure there
has to be 10 letters so 5 is not accepted!

Thank You

In a nutshell


forloop

cin>>array[variable];


Is there an API describing C++ functions?

Could you not just do something like this

Code:

char variable[];

I think this would make it so that it would go to whatever length the cin uses.

>I think this would make it so that it would go to whatever length the cin uses.
Nope, that's an array without a size which is illegal unless it's an extern declaration defined elsewhere. You must specify a size for built-in arrays, that's one reason the vector class is so useful: You can have variable length vectors without having to worry about memory management. It's a win-win situation.

how do i find out more about vectors and the cin function?

I absolutely agree that using the string class is preferred over using C style char arrays. You still might need to only read in a certain number of characters if you use strings, though. Here is another way to do that that works with strings or char arrays:

Code:

#include <iostream>
#include <string>
#include <iomanip>

int main()
{
    int numLettersToRead = 5;
    char chArray[10];
    std::string stdString;

    // Use numLettersToRead+1 to allow for the null character
    // that is automatically tacked on.
    std::cin >> std::setw(numLettersToRead+1) >> chArray;

    // Use numLettersToRead since you don't have to worry about
    // the null terminator with the string class.
    std::cin >> std::setw(numLettersToRead) >> stdString;

    std::cout << chArray << std::endl;
    std::cout << stdString << std::endl;

    return 0;
}

Of course, if you don't like all the std:: things everywhere, you can remove them and put using namespace std; after the #include's.

I 've seen/read many arguments for learning C++ strings from the beginning (as well as other STL stuff like vectors), including a paper by Stroustrup. Those arguments make sense to me. The only valid argument I've heard for learning C-style strings first is that eventually a good programmer should know how that stuff works. That makes sense, but doesn't seem as important in my mind as learning the new/preferred way to do things.

Here is Stroustrup's comments:
http://www.research.att.com/~bs/new_learning.pdf