Reverse Polish Notation

[cooolio]

Im having trouble grasping the concept of RPN. I have to read it and evaluate using stack

  // im reading it in as a string
         string prefix;
	cout << "Enter: ";
	cin >> prefix;
 // then I convert it to integer
      atoi(prefix.c_str())
 

but then how do i differentiate from a number and an operand?
Any help would be appreciated

[cooolio]

so nothing?

[coder777]

lookt at the reference of ctype, like this:

http://www.cplusplus.com/reference/cctype/isdigit/

you need a loop for your string prefix:

for(size_t i = 0; i < prefix.size(); ++i)
{
  if(isdigit(prefix[i]))
    ...
  else if('+' == prefix[i])
    ...
  else
}

[cooolio]

ok thanks for pushing me in the right direction coder777

if(isdigit(prefix[i]))
{
 stack.push(prefix);
}
else if('+' == prefix[i])
{
operandstack.push(prefix);
}
else if('-' == prefix[i])
.
.
.

would it be something like that?

[cooolio]

can someone help me convert this to take n amount of numbers.

double value1; double value2, value3;

				if('+' == str[i])
					{ 
						value2 = calculate.top();
						calculate.pop();
						value1 = calculate.top();
						calculate.pop();
						value3 = calculate.top();
						calculate.pop();
						calculate.push(value1 + value2 + value3);
						cout << "no" ;
					}
					else if('-' == str[i])
					{
					
						value2 = calculate.top();
						calculate.pop();
						value1 = calculate.top();
						calculate.pop();
						calculate.push(value1- value2);
					}
					else if( '*'== str[i])
					{
						value2 = calculate.top();
						calculate.pop();
						value1 = calculate.top();
						calculate.pop();
						calculate.push(value1*value2);
					}
					else if( '/' == str[i])
					{
						value2 = calculate.top();
						calculate.pop();
						if (value2 == 0)
						{undefined = true;}
					
					else
					
						value1 = calculate.top();
						calculate.pop();
						calculate.push(value1 / value2);
					
					}