Data in string stream

Sephiron (11)
I'm doing a program that work out "Reverse Polish Notation" algorithm. Part of my code is this:

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while( !queue.empty() )
	{
		token = queue.front();
		queue.pop();
		if( isdigit(token[0]) )
			stack.push(token);
		else
		{
			opr1.clear();
			opr2.clear();
			opr1 << stack.top();
			stack.pop();
			opr2 << stack.top();
			stack.pop();
			opr1 >> x;
			opr2 >> y;
			result = new stringstream;
			switch( token[0] )
			{
				case '+': *result << y + x;
					break;
					
				case '-': *result << y - x;
					break;
					
				case '*': *result << y * x;
					break;

				case '/': *result << y / x;
					break;
			}
			stack.push( result->str() );
			delete result;
		}
	}


It works correctly. However, if I were to change the result variable from type stringstream* to stringstream, it wouldn't work correctly anymore. Assuming in the first while loop, operation between y and x produces "2" (push "2" to stack thanks to result.str() ) and in the second time the loop executes, the operation produces "-3", then the thing being pushed to stack the second time is "2-3" and not just "-3".

I tried .flush() and .clear() but both didn't work out for me, so I had to resort to new-ing and deleting a pointer everytime.

Why do opr1 and opr2 (of type stringstream) can get data from stack and extract them to x and y correctly, but not the result?

My previous attempt (which is wrong and didn't work) is something like this:

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while( !queue.empty() )
	{
		token = queue.front();
		queue.pop();
		if( isdigit(token[0]) )
			stack.push(token);
		else
		{
			opr1.clear();
			opr2.clear();
			result.clear();
			result.flush();
			opr1 << stack.top();
			stack.pop();
			opr2 << stack.top();
			stack.pop();
			opr1 >> x;
			opr2 >> y;
			switch( token[0] )
			{
				case '+': result << y + x;
					break;
					
				case '-': result << y - x;
					break;
					
				case '*': result << y * x;
					break;

				case '/': result << y / x;
					break;
			}
			stack.push( result.str() );
			delete result;
		}
	}


Any input as to why the problem occurred as well as how to make this part looks less like a mess, is really appreciated.

Thanks in advance.
webJose (2948)
The problem relies in the place where "result" is declared. It is most likely declared outside the function that contains this piece of code. If you delete the current definition of "result", you can then exchange line 17 in your first code block to:

stringstream result;

And now you can forget about new and delete.

opr1 and opr2 do not accumulate because they are "discharging" their contents into variables x and y all the time.
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