Reading in an unknown number of numbers

I hit a little barrier while trying to implement an RPN calculator today. I want to have expressions like this in a file:

Code:

33 10 +

But that could be any number of numbers and I have no idea how to read them in.

Code:

int main (int argc, char *argv[])
{
        FILE            *f = 0;
        int             ch = 0;
        Stack           *stk = new Stack (256);

        f = fopen ("z:\\test.rpn", "r");
        if (! f) {
                cout << "Error opening file\n";
                return 1;
        }

        while ((ch = fgetc (f)) != EOF) {  // The offending line
                switch (ch) {
                        case '+': {
                                        char    one, two, ans;

                                        one = stk->pop ();
                                        two = stk->pop ();
                                        ans = one + two;
                                        stk->push (ans);

                                        break;
                                  }
                        case '-':
                                break;
                        case '/':
                                break;
                        case '*':
                                break;
                        default: // assumed to be a literal to push
                                stk->push (ch);
                }
        }

        fclose (f);
        delete stk;
         return 0;
}

I don't have a clue how to read in an unknown number of numbers, as the title suggests.

from the tutorial:

Code:

#include <fstream>
#include <iostream>

using namespace std;

int main()
{
  char str[10];

  //Creates an instance of ofstream, and opens example.txt
  ofstream a_file ( "example.txt" );
  // Outputs to example.txt through a_file
  a_file<<"This text will now be inside of example.txt";
  // Close the file stream explicitly
  a_file.close();
  //Opens for reading the file
  ifstream b_file ( "example.txt" );
  //Reads one string from the file
  b_file>> str;
  //Should output 'this'
  cout<< str <<"\n";
  cin.get();    // wait for a keypress
  // b_file is closed implicitly here
}

put the reading from the file in a loop terminating at eof (or your own terminator), convert the read data to integers, and away you go.

But that could be any number of numbers

The data is delineated by spaces, so you can read them in one at a time until there aren't anymore. The most efficient way to read them in is by reading in the whole line at one shot, and then using your program to separate out the pieces. Because you have numbers and characters intermixed in the data, you have to read the whole thing in as a string, so the trick is being able to convert the pieces of the string that are numbers to numeric types. In C++, you can use stringstreams to do that, e.g.

Code:

#include <iostream>
#include <string> //string type, find()
#include <cctype> //isdigit()
#include <sstream> //istringstream

using namespace std;


int main()
{
	string data = "30 10 + 20 -";

	int start = 0;
	int pos = data.find(" ", start);

	string piece = data.substr(start, pos - start);
	
	double theNum = 0.0;
	if(isdigit(piece[0]))
	{
		istringstream inStr(piece); //creates a "stringstream" from which 
                                            //you can read data into any type using >>
		inStr>>theNum;
	}

	cout<<theNum<<endl;
	cout<<theNum + 10.0<<endl;  //to prove theNum is a numeric type

	return 0;
}

When you eventually get this far...

Calculator program

Good luck