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);
    }

Code:

while (coin !=0);

When will that ever happen?

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

Yeah, but coin is a pointer to a string. Why would it ever be 0?

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

Off the top of my head:

Code:

while(std::cin.get() != '0')

> 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.