infix to postfix with logical operators - code error - c++

Question

i m trying to Write a function string InfixToPostfix(string infixExpr) that takes as input an expression string in infix notation, and returns a string containing the postfix notation for that expression. The infix notation can have
parenthesis. The program needs to handle these operators ∗,/, %, +, − , <, <=, >=, >, ==, ! =,&&,|| (binary operators only)
Here is the code i am trying.. its running perfect with parenthsis but gives slight wrong output without parenthesis. e.g if input is A+B/C the output should be ABC/+, but instead it gives AB+C/ . please help me spot the error. Thanks
#include<iostream>
#include<stack>
#include<string>
using namespace std;
// Function to convert Infix expression to postfix
string InfixToPostfix(string expression);
// Function to verify whether an operator has higher precedence over other
int HasHigherPrecedence(string operator1, string operator2);
// Function to verify whether a character is operator symbol or not.
bool IsOperator(string C);
// Function to verify whether a character is alphanumeric character (letter) or not.
bool IsOperand(string C);
int GetOperatorWeight(string opt);
bool IsDoubleOperator(char c1, char c2);
int main()
{
string expression;
cout<<"Enter Infix Expression \n";
getline(cin,expression);
string postfix = InfixToPostfix(expression);
cout<<"Output = "<<postfix<<"\n";
return 0;
}
// Function to evaluate Postfix expression and return output
string InfixToPostfix(string expression)
{
// Declaring a Stack from Standard template library in C++.
stack<string> S;
string postfix = ""; // Initialize postfix as empty string.
for(int i = 0;i< expression.length();i++) {
string ex="";
ex+=expression[i];
// Scanning each character from left.
// If character is a delimitter, move on.
if(ex == " " || ex == ",") continue;
// If character is operator, pop two elements from stack, perform operation and push the result back.
else if(IsOperator(ex))
{
while(!S.empty() && S.top() != "(" && HasHigherPrecedence(S.top(),ex))
{
postfix+= S.top();
S.pop();
}
S.push(ex);
}
// Else if character is an operand
else if(IsOperand(ex))
{
postfix +=ex;
}
else if (ex == "(")
{
S.push(ex);
}
else if(ex == ")")
{
while(!S.empty() && S.top() != "(") {
postfix += S.top();
S.pop();
}
S.pop();
}
else if (IsDoubleOperator(expression[i], expression[i+1]))
{
string db="";
string f="";
db=+expression[i];
f=+expression[i+1];
db=db+f;
while(!S.empty() && S.top() != "(" && HasHigherPrecedence(S.top(),db))
{
postfix+= S.top();
S.pop();
}
S.push(db);
i++;
}
}
while(!S.empty()) {
postfix += S.top();
S.pop();
}
return postfix;
}
// Function to verify whether a character is english letter or numeric digit.
// We are assuming in this solution that operand will be a single character
bool IsOperand(string C)
{
if(C >= "A" && C <= "Z") return true;
return false;
}
// Function to verify whether a character is operator symbol or not.
bool IsOperator(string C)
{
if(C == "+" || C == "-" || C == "*" || C == "/" || C== "%")
return true;
return false;
}
// Function to get weight of an operator. An operator with higher weight will have higher precedence.
int GetOperatorWeight(string op)
{
int weight = -1;
if(op=="&&"|| op=="||")
weight = 1;
if(op=="=="|| op=="!=")
weight = 2;
if(op=="<"|| op==">"|| op=="<="|| op==">=")
weight = 3;
if(op=="+"|| op=="-")
weight = 4;
if(op=="/"|| op=="%"|| op=="/")
weight = 5;
return weight;
}
// Function to perform an operation and return output.
int HasHigherPrecedence(string op1, string op2)
{
int op1Weight = GetOperatorWeight(op1);
int op2Weight = GetOperatorWeight(op2);
// If operators have equal precedence, return true if they are left associative.
// return false, if right associative.
// if operator is left-associative, left one should be given priority.
if (op1Weight > op2Weight)
return op1Weight;
else
return op2Weight;
}
bool IsDoubleOperator( char c1, char c2)
{
string db="";
string f="";
db=+c1;
f=+c2;
db=db+f;
if (db=="&&" ||db=="||" || db==">=" || db=="<=" || db=="!=" ||db=="==")
{
//cout<<db;
return true;
}
return false;
}

Answer 1

HasHigherPrecedence(op1, op2) is expected to return non-zero when op1 has a higher precedence (A.K.A. weight) than op2 and zero otherwise. However it returns the maximum of the two ops' weights, which is usually nonzero. You just need to change the function so it returns:
return op1Weight > op2Weight;
Which will be 1 when true and zero when false. This should fix your operator shunting.