Ignoring puncuations in input stream

This is a discussion on Ignoring puncuations in input stream within the C++ Programming forums, part of the General Programming Boards category; hello, this is my first post, nice to meet everyone I am taking input from the keyboard, and I want ...

  1. #1
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    Ignoring puncuations in input stream

    hello, this is my first post, nice to meet everyone

    I am taking input from the keyboard, and I want to ignore
    whitespace, punctuation and the case of letters, i.e. 'a' = 'A'

    I figured out the whitespace, but I can't figure out letter case and
    punctuation. Here is my code (my main function, which uses a stack
    and queue objects). The program is meant to determine whether or
    not a statement is a palindrome.

    Code:
    #include "stack.h"
    #include "queue.h"
    #include <iostream>
    
    using namespace std;
    
    int main()
    {
        bool isPalindrome = true;
        char ch, ch1, ch2;
        StackType s;
        QueueType q;
    
        cout << "Enter a statement: ";
    
        cin >> ch;
        while(!s.IsFull() && ch != '\n')
        {
            s.Push(ch);
            q.Enqueue(ch);
            if(cin.peek() != '\n')
                cin >> ch;
            else
                cin.get(ch);
        }
    
        while(isPalindrome && !s.IsEmpty())
        {
            q.Dequeue(ch1);
            ch2 = s.Top();
            s.Pop();
            isPalindrome = ch1 == ch2;
        }
    
        cout << endl;
    
        if(isPalindrome)
            cout << "Entered statement is a Palindrome\n";
        else
            cout << "Entered statement is not a Palindrome\n";
        return 0;
    }
    thanks!

  2. #2
    Deathray Engineer MacGyver's Avatar
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    Some useful things from working a bit with assembly:

    • To guarantee a char will be lowercase you can OR it with 0x20.
    • To guarantee a char will be uppercase, you can AND with 0xDF.

  3. #3
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    You can't handle case and punctuation with the input stream, you have to read in the character first and then handle them.

    You can use tolower and/or toupper to change the case of a character. You can use ispunct to check to see if the character is punctuation and skip it if it is.

    >> Some useful things from working a bit with assembly
    Those might be useful for a code obfuscation contest, but for a real program I would use tolower and toupper.

  4. #4
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    thank you, everything works, but for the tolower function,
    it returns the ASCII value for the char. Is there any way I can
    change that value back to the char instead of an ASCII int?

    thanks again

  5. #5
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    Simply assign it to a char variable and it will be converted correctly.

    If you want to avoid a warning, just use a cast. The C++ style cast is:
    Code:
    ch = static_cast<char>(::tolower(ch));

  6. #6
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    What's the difference between "::tolower" and "tolower"?
    Are they located in different libraries or namespaces?

    I just tried them out and they give different outputs for the following lines of code:
    Code:
    char c;
    ...
    cout << hex << tolower(c) << endl;
    cout << hex << ::tolower(c) << endl;
    The upper output is hexadecimal, the lower is plain decimal. Why is that?
    Last edited by cunnus88; 03-30-2007 at 11:33 PM.

  7. #7
    Registered User Noir's Avatar
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    What's the difference between "::tolower" and "tolower"?
    Depends on how your header files and namespace stuff is set up:
    Code:
    #include <ctype.h>
    
    // both are the same because tolower() is in the global namespace
    cout << hex << tolower(c) << endl;
    cout << hex << ::tolower(c) << endl;
    Code:
    #include <cctype>
    
    // both are wrong because tolower() is in the std namespace; might not compile
    cout << hex << tolower(c) << endl;
    cout << hex << ::tolower(c) << endl;
    Code:
    #include <cctype>
    
    using namespace std;
    
    // this one is right because it's defaulted to the std namespace
    cout << hex << tolower(c) << endl;
    
    // this one is not because tolower() is in the std namespace; might not compile
    cout << hex << ::tolower(c) << endl;

  8. #8
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    What's the difference being "defaulted" to the std namespace and being "in" the namespace?

    In other words, what does "::" do, when it doesn't have a scope modifier (as in class A::B)?

  9. #9
    Registered User Noir's Avatar
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    What's the difference being "defaulted" to the std namespace and being "in" the namespace?
    Nothing. "defaulted" means that you said 'using namespace std' or 'using std::tolower' and from then on every tolower() becomes std::tolower() by default.
    In other words, what does "::" do, when it doesn't have a scope modifier (as in class A::B)?
    It's explicitly saying that the thing is in the global namespace.

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