Infix to Postfix - Deleting Parenthesis - c++

Question

Having trouble getting the parenthesis to pop from the string.
I enter an infix expression such as (A+B)*C and would like to get AB+C*.
Instead, I get (AB)+C*. Any help would be greatly appreciated.
string Postfx::convertToPostfix(Postfx C,string in)
{
stack<char> S;
string postfx = "";
for (int i = 0; i<in.length();i++)
{
if (in[i] == ' ' || in[i] == ',') continue;
else if ((in[i]) == '+' || in[i] == '-' || in[i] == '/' || in[i] == '*')
{
while (!S.empty() && S.top() != '(' && C.precedence(S.top(), in[i]))
{
postfx += S.top();
S.pop();
}
S.push(in[i]);
}
else if ((in[i]) != '+' || in[i] != '-' || in[i] != '/' || in[i] != '*')
{
postfx += in[i];
}
else if (in[i] == '(')
{
S.push(in[i]);
}
else if (in[i] == ')')
{
while (!S.empty() && S.top() != '(')
{
postfx += S.top();
S.pop();
}
S.pop();
}
}
while (!S.empty()) {
postfx += S.top();
S.pop();
}
return postfx;
}

Answer 1

I think that your
else if ((in[i]) != '+' || in[i] != '-' || in[i] != '/' || in[i] != '*')
line catches brackets as well, so
else if (in[i] == '(')
and below never gets executed.
I think you should move
else if ((in[i]) != '+' || in[i] != '-' || in[i] != '/' || in[i] != '*')
to be the last option in the chained if.
Moreover, this if catches absolutely any symbol (because any symbol is either not equal to '+', or not equal to '-'). You need to replace || by &&; but if you will anyway have this if the last in chained if, you need no condition there at all, something like:
if ((in[i] == ' ')|| ...
else if ((in[i] == '+')|| ...
else if (in[i] == '(') ...
else if (in[i] == ')') ...
else postfx += in[i]; // no condition here
P.S. Also if you wrap the initial expression in brackets:
in = "(" + in + ")"
before the loop, you will not need the final while (!S.empty()) loop.

Answer 2

Don't append the parentheses to the output. They're only in the stack to guide your actions. I don't know where you got this code but you need to take a good look at the Dijkstra Shunting-yard algorithm. Your version doesn't match it at several points, and some of it doesn't even make sense:
if (in[i] != '+' || in[i] != '-' || in[i] != '/' || in[i] != '*')