Polish.h
class polish{
	 double eval;
	 char* infix;
	 char* postfix;
	 int priority(char ch);
	 int isOperator(char ch);
	 int operate(int a, int b, char op);
	 int caracter(char c);
public:
	polish(char *ch);
	void ReversePolishNotation();
	void ReversePolishEvaluate();
};


Polish.cpp
#include<stdio.h>
#include<string.h>
#include<iostream.h>

polish::polish(char *ch)
{
   strcat(infix,ch);
}

int polish::priority(char ch)
{  if (ch=='*') return 3;
   if (ch=='/') return 4;
   if (ch=='+') return 1;
   if (ch=='-‘) return 2;
   return 0;
}


int polish::isOperator(char c)
{ if(priority(c)>0)   return 1;
  else return 0;
}

int polish::caracter(char c)
{ int ret;
	if (c== '0') ret=0;
	if (c== '1') ret=1;
	if (c== '2') ret=2;
	if (c== '3') ret=3;
	if (c== '4') ret=4;
	if (c== '5') ret=5;
	if (c== '6') ret=6;
	if (c== '7') ret=7;
	if (c== '8') ret=8;
	if (c== '9') ret=9;
	return ret;
}

void polish::ReversePolishNotation()
{ int i;
  char *ret;
  ret="";
  char c;
  char st[10];
  int top=-1;
  i=0;
  while(i<strlen(infix))
	{  if(!isOperator(*(infix+i)))
			  ret=ret+(*(infix+i));
	else{
        while((top>=0)&&(priority(st[top])>=priority(*(infix+i))))
				 { c=st[top];
				   top--;
				   ret+=c;
				 }
 	     top++;
		st[top]=*(infix+i);
	}
	  i++;
	 }
	while(top>=0)
	  { c=st[top];
	    top--;
	    ret+=c;
	  }
	postfix=ret;
	cout<<ret;
}

int polish::operate(int a, int b, char op)
{ int rez;
  if (op=='+') rez=a+b;
  if (op=='-') rez=a-b;
  if (op=='*') rez=a*b;
  if (op=='/') rez=a/b;
  return rez;
}

void polish::ReversePolishEvaluate()
{  int st[10];
	int a,b;
	int i,top=-1;
	i=0;
	while(i<strlen(postfix))
	 { if(isOperator(*(postfix+i)))
			{ b=st[top];
			  top--;
			  a=st[top];
			st[top]=operate(a,b,*(postfix+i));
			}
		else
	  {
		top++;
		st[top]=caracter(*(postfix+i));
	  }
		i++;
	 }
  eval=st[top];
  cin>>eval;
}


exPolish.cpp
void main(){
	char *sir;
	cout<<"Introduceti expresia de evaluat"<<endl;
	cin>>sir;
	polish p(sir);
	p.ReversePolishNotation();
	p.ReversePolishEvaluate();
}