Thread: Stringy Sums

Say I had:

Code:

(6/2*(3+4))/6

all stored in a string...would it then be possible me to calculate that sum in any way?

Do a board search for "reverse polish"

Or a Google™. There's also this nifty site called "Wikipedia", rings a bell?

Yep...I looked at the stuff on Wikipedia asked my Dad as he is a fair good Maths person and I understand how you order it...but how do you get a program to output say 3+4-

No I mean how can I get the result of the sum I can think of ways in which I could convert to RPN but not to do the sum.

I don't really get you there...I will have all of my stuff stored in a string.

Well what I have is theuser inputting their equation into a string and then it is converting it to RPN.

Well I may be completely wrong but I haven't quite finished the code

Code:

#include <iostream>
#include <string>
#include <cstdlib>

using namespace std;

int main()
{
      string sum = "";
      string output= "";
      string stack = "";

      cout << "Please type in your sum: ";
      getline(cin, sum);

      for (int i = 0; i < sum.length(); i++) {
      char x = sum.at(i);
      switch (x) {
      case '1':
           output += x;
           break;
      case '2':
           output += x;
           break;
      case '3':
           output += x;
           break;
      case '4':
           output += x;
           break;
      case '5':
           output += x;
           break;
      case '6':
           output += x;
           break;
      case '7':
           output += x;
           break;
      case '8':
           output += x;
           break;
      case '9':
           output += x;
           break;
      case '0':
           output += x;
           break;
      case '+':
           stack += x;
           break;
      case '-':
           stack += x;
           break;
      case '*':
           stack += x;
           break;
      case '/':
           stack += x;
           break;
      default :
           cout << "Error with input";
           cin.ignore();
           cin.get();
           return 0;
      }
      }
      output += stack;
      cout << output << endl;
      system("PAUSE");
      return 0;
}

That is what I have done...I may be wrong in what I have done and I have yet to add parenthesis

Code:

case ')':
           int z;
           z = sum.find_last_of('(', 0);
           int n;
           n = ++z;
           output += sum.substr(n);
           sum.erase(z);
           break;

It seems to delete the wrong part of the string when I try that...why?

How can I get it to delete the bit on the end that I need to get rid of.

Ok. If I was going to do this, I would do it this way:

Code:

#include <iostream>
#include <string>
#include <cstdlib>

using namespace std;

int main()
{
	string sum = "";

	cout<< "Please type in your sum: ";
	cin >> sum;

	int         x = 0;
	double output = 0;

	for (int i = 0; i < sum.length(); i++) 
	{
		x = sum.at(i);

		switch ( x ) 
		{
			case '1':
				output += ( x - '0');
				break;

			case '2':
				output += ( x - '0');
				break;

			case '3':
				output += ( x - '0');
				break;

			case '4':
				output += ( x - '0');
				break;

			case '5':
				output += ( x - '0');
				break;

			case '6':
				output += ( x - '0');
				break;

			case '7':
				output += ( x - '0');
				break;

			case '8':
				output += ( x - '0');
				break;

			case '9':
				output += ( x - '0');
				break;

			case '0':
				output += ( x - '0');
				break;


			case '+':
				output += ( sum[i+1] - '0' );
				
				i++;
				break;

			case '*':
				output *= ( sum[i+1] - '0' );
				
				i++;
				break;

			default :
				cout << "Error with input";
				cin.ignore();
				cin.get();
				return 0;
		}
	}

	cout << output << endl;

	return 0;
}

This works, but it doesn't have any hierarchy of operators, if you know what I mean. It just works from the left hand side to the right hand side.

This is essentially your code, but the changes I made were that the output is an integer (it'd probably be better to have a float or something), and in all the operators, because the input is a string, I subtracted '0' from it ... ie:

Code:

'1' = 31 (from memory, so it's prob wrong), in ASCII,
'1' - '0' = 1 in ascii.
int Var = '1' - '0';

cout<< Var;

Output: 1

get me?