#include <iostream>
#include <string>
#include <stack>
#include <cctype> //alnum
#include <cassert> //assert
using namespace std;
#include <sstream>
string infixTOposfix(string);
int evaluarRPN(string);
int main ()
{ // main began
string infix,
posfixWspaces,
dummy;
double result;
char repeat;
do {
cout << "\nPlease enter the expression in INFIX: ";
getline(cin,infix);
posfixWspaces = infixTOposfix(infix);
cout << "This is the expression in POSTFIX: " << posfixWspaces << endl;
result = evaluarRPN(posfixWspaces);
cout << "The expression after the evaluation: " << result;
cout << "\nDo you want to repeat? Enter 'y' ";
cin >> repeat;
getline(cin,dummy);
} while ( repeat == 'y');
system("PAUSE");
return 0;
} // main end
string infixTOposfix(string exp)
{
/*-------------------------------------------------------------------------
Function to convert an infix expression exp to postfix.
Precondition: None
Postcondition: Postfix expression corresponding to exp is returned
or an error message displayed if exp is not well-formed.
-------------------------------------------------------------------------*/
char token, // character in exp
topToken; // token on top of opStack
stack<char> opStack; // stack of operators
string postfixExp; // postfix expression
const string BLANK = " ";
for (int i = 0; i < exp.length(); i++)
{
token = exp[i];
switch(token)
{
case ' ' : break; // do nothing -- skip blanks
case '(' : opStack.push(token);
break;
case ')' : for (;;)
{
assert (!opStack.empty());
topToken = opStack.top();
opStack.pop();
if (topToken == '(') break;
postfixExp.append(BLANK + topToken);
}
break;
case '+' : case '-' :
case '*' : case '/': case'%':
for (;;)
{
if (opStack.empty() ||
opStack.top() == '(' ||
(token == '*' || token == '/' || token == '%') &&
(opStack.top() == '+' || opStack.top() == '-'))
{
opStack.push(token);
break;
}
else
{
topToken = opStack.top();
opStack.pop();
postfixExp.append(BLANK + topToken);
}
}
break;
default : // operand
postfixExp.append(BLANK + token);
for(;;)
{
if ( !isalnum(exp[i+1]) ) break; // end of identifier
i++;
token = exp[i];
postfixExp.append(1, token);
}
}
}
// Pop remaining operators on the stack
for (;;)
{
if (opStack.empty()) break;
topToken = opStack.top();
opStack.pop();
if (topToken != '(')
{
postfixExp.append(BLANK + topToken);
}
else
{
cout << " *** Error in infix expression ***\n";
break;
}
}
return postfixExp;
}
int evaluarRPN(string posfijo)
{ // evaluarRPN began
stack<int> numStack;
int x,
y,
toInt;
string number;
for (int i = 1; i < posfijo.length(); i++)
{ // for began
if ( isdigit(posfijo[i]) )
{ // if began
number = posfijo[i];
stringstream ss( number );
ss >> toInt;
numStack.push( toInt );
} // if end
else if (posfijo[i] != ' ' )
{ // else began
y = numStack.top();
numStack.pop();
x = numStack.top();
numStack.pop();
if (posfijo[i] == '+')
numStack.push( x+y );
else if (posfijo[i] == '-')
numStack.push( x-y );
else if (posfijo[i] == '*')
numStack.push( x*y );
else
numStack.push( x/y );
} // else end
} // for end
return numStack.top();
} // evaluarRPN endthat is the code.... I only works in a single digit... Can anyone help me or give me a tip of including exponents, decimals and more than one digit value?
