Help with isdigit and for loops

This is a discussion on Help with isdigit and for loops within the C++ Programming forums, part of the General Programming Boards category; I am attempting to check whether a number entered is a digit. I have devised that the way to do ...

  1. #1
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    Angry Help with isdigit and for loops

    I am attempting to check whether a number entered is a digit. I have devised that the way to do this is to create a character array and save the user input there. Then I open/create a text file. USing a for loop I check that they are all digits. If they are my main program should continue on the return of the value 1 in "digit".



    It took me ages to get the open/write/read file to work and now my program does the loop but makes me input too many numbers and wont move on. The user must be able to input a figure of up to 3 digits... If someone could help I would be extremely grateful... I may even send flowers....


    Code:
    int coincheck(void)
    
    {
       ofstream outfile("c:\data.txt",ios::out); //creates outfile
       if(!outfile)
         {
            cerr<<"error:cant open\n";
            exit(1);
          }
        //cout<<"please enter your coin.\n";
        cin>>coin;
        cout<<"\n!!! - "<<coin;
        do{
                for (i=0;(c=getchar()) != '\n';++i)
                   {
                       coin[i] = c;
                       if(isdigit(c))
                            {
                                 cout<<"gifgvhcfj";
                                 outfile<<c;
                                 digit=1;
                             }
                       else
                            {
                                 cout<<"must be a number/n";
                                 digit=0;
                                 exit(1);
                            }
                     }
          outfile.close();
         }while (coin !=0);
       ifstream infile("c\data.txt",ios::in); //opens file
       if(!outfile)
          {
              cerr<<"error:cant open\n";
              exit(1);
           }
        infile>>newcoin;
        infile.close();
        return (0);
        exit(1);
        }

  2. #2
    Registered User Tonto's Avatar
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    Code:
    while (coin !=0);
    When will that ever happen?

  3. #3
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    Sorry... What I should have told you is that this is a function in a much bigger program that I am writing. The user has to enter on of 5 coin choices 5, 10, 20, 50, 100. To terminate this loop they are to simply enter 0. I am okay checking the values in my main with an if statement using a lot of OR's but decided to write a function to check if it was a digit to stop people inputting letters. Another problem I have is with my for loop... it goes on for too long if they just want to enter the number 5

  4. #4
    Registered User Tonto's Avatar
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    Yeah, but coin is a pointer to a string. Why would it ever be 0?

  5. #5
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    OKAY!!! So how do I say "While the user has not entered the value '0' "? Coin was an int before I changed it to a pointer so I thought it would work... I thought wrong

  6. #6
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    Off the top of my head:
    Code:
    while(std::cin.get() != '0')

  7. #7
    and the hat of int overfl Salem's Avatar
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    > ofstream outfile("c:\data.txt",ios:ut);
    Don't forget, to get a single \, you must write \\

    > ifstream infile("c\data.txt",ios::in);
    Missing : as well.
    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.

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