Experts please help a student! Basic C++ question.

This is a discussion on Experts please help a student! Basic C++ question. within the C++ Programming forums, part of the General Programming Boards category; this is a part of my programme Code: class Impedence { protected: int R1, R2, X1, X2; public: void enterNum(void); ...

  1. #1
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    Experts please help a student! Basic C++ question.

    this is a part of my programme

    Code:
    class Impedence
    {
    protected:
        int R1, R2, X1, X2;   
    public:
    	void enterNum(void);
    };
    void Impedence::enterNum(void)
    {
    
            cout<<"Enter real part of impendence A: ";
    	cin>>R1;
            cout<<"Enter imaginary part of impedence A: ";
    	cin>>X1;
    	cout<<"Enter real part of impedence B: ";
    	cin>>R2;
    	cout<<"Enter imaginary part of impedence B: ";
    	cin>>X2;
    }
    how do i modify it such that the user can only enter positive integer?
    invalid input will stop the next statement and return to the first.
    for eg. if the user entered alphabet "a" or any other alphabet it will show "Please enter an integer value!" the programme will then loop back to the first cout.
    Last edited by goodgene; 08-13-2011 at 10:17 AM.

  2. #2
    and the hat of wrongness Salem's Avatar
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    Read your book on do...while loops perhaps?
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  3. #3
    and the Hat of Guessing tabstop's Avatar
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    If you are worried about people typing letters instead of numbers, then you need to look at methods for getting rid of input (>> will absorb -1 and allow you to get rid of it, but a will stay forever). You can either read into a string and then parse the string, or you can check whether the input stream is in a fail state using fail() and then clear the input stream.

  4. #4
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    It may also be better, in this case, to read a whole line of input into a string (using istream's getline() method), interpret the input to see if it is valid, and only then extract the values needed

    Also, if you want to input a positive value, why not store it in an unsigned type?
    Right 98% of the time, and don't care about the other 3%.

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