C++ Cin Help!

This is a discussion on C++ Cin Help! within the C++ Programming forums, part of the General Programming Boards category; Hello, I have a problem while CIN into an array of Chars. Say If I declare an array of Chars ...

  1. #1
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    Unhappy 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

  2. #2
    Registered User axon's Avatar
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    show us your code, and try using getline function with the length parameter....

    axon

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    In a nutshell


    forloop

    cin>>array[variable];


    Is there an API describing C++ functions?

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    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.

  5. #5
    twm
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    >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.

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

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    vectors are part of the standard template library, just look that up in google

    If you are going to use vectors then you might as well use strings to not c style strings.

    Strings are part of the standard template library as well and safer especially for dynamicaly allocation.

    I have read in many post that learning about string objects is more important than the deprecated charachter arrays or c style strings. The main reason for learning about c style strings is for the massive amounts of legacy code still in use, but shouldn't generally be used in modern c++ programs.(This is probably gonna get me flamed.)

    cin.getline(array,SIZE);

    will extract charachters from the input stream up to a maximum number of chars-1 specified by SIZE. Note

    cin.get(array,SIZE,'\n');
    reads charachters from the input stream terminates at 1-SIZE or when the delimeter is entered in this case '\n'

    I believe input past the size as prompted by cin stays in the input stream and must be read or ignored.
    cin.ignore();
    Last edited by curlious; 09-15-2003 at 12:40 PM.

  8. #8
    Registered User jlou's Avatar
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    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.

  9. #9
    Registered User axon's Avatar
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    Originally posted by jlou
    I absolutely agree that using the string class is preferred over using C style char arrays.
    Yes,but it looks like this is an intro c++ course or book...so using cstrings makes the student understand more of what is actually going on. In my intro c++ course we didn't use strings literals until the very end...

    axon

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    there are two cardinal sins from which all others spring: Impatience and Laziness. - franz kafka

  10. #10
    Registered User jlou's Avatar
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    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

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