Simple Infix to Postfix in C++

Converting an Infix expression to postfix is not a big deal. Even though for a beginner it could be frustrating for hours.

Enough breaking your computers. Its time to finish it off!.

Infix expression:

     The Infix expressions are the expressions which we usually use in mathematical form.

Eg: a*(b+d*c)

Postfix expression:

     These expressions are used by the computer to evaluate the given infix expressions. They simply convert infix expression to postfix using stack data structure.

Eg: a b d c * + *

Stack data structure is pre-request for this conversion which we will not discuss here. Just google it for more information.

I have written a simple program for this conversion process. Almost it is self explanatory. Share if you like this.

	#include<iostream>
	#include<stack>//import Stack STL
	#include<string>//import String STL
	#include<conio.h>
	using namespace std;
	string infixToPostfix(string expr); //Function declaration
	int precendence(char arg);
	bool isoperand(char arg);
	bool isoperator(char arg);
	int operatorweight(char arg);
	bool highprecendence(char a, char b);
	int main()
	{
	string exp;//Variable to get input expression
	cout<<"Enter the infix expression:";
	getline(cin,exp);
	cout<<"Output Postfix Expression:"<<infixToPostfix(exp);
	getch();
	}
	string infixToPostfix(string expr)//Function to perform all conversion operation
	{
	stack<char> stk;//Declaring a stack for conversion purpose
	string postfix = "";//Initialize the output string as empty;
	for(int i = 0;i < expr.length(); i++)//Scan the infix string one by one
	if(expr[i] == '(')
	{
	stk.push(expr[i]);
	}
	else if(expr[i] == ')')
	{
	while(stk.top() != '(')
	{
	postfix = postfix + stk.top();
	stk.pop();
	}
	stk.pop();
	}
	else if(isoperand(expr[i]))
	{
	postfix += expr[i];
	}
	else if(isoperator(expr[i]))
	{
	while(!stk.empty()&& !highprecendence(expr[i],stk.top()))
	{
	postfix+= stk.top();
	stk.pop();
	}
	stk.push(expr[i]);
	}
	while(!stk.empty())
	{
	postfix+= stk.top();
	stk.pop();
	}
	return postfix;
	}
	bool highprecendence(char a, char b)//Check for operator precendence
	{
	int weighta = operatorweight(a);
	int weightb = operatorweight(b);
	if(weighta >= weightb) return 1;
	return 0;
	}
	bool isoperator(char arg)//Check weather the character is operator
	{
	if(arg == '*' || arg == '/' || arg == '+' || arg == '-') return(1);
	else return(0);
	}
	bool isoperand(char arg)//Check weather the character is operand
	{
	if(arg >= '0' && arg <= '9') return 1;
	if(arg >= 'a' && arg <= 'z') return 1;
	if(arg >= 'A' && arg <= 'Z') return 1;
	return 0;
	}
	int operatorweight(char arg)//Add weight to the operator
	{
	int weight = 0;
	switch(arg)
	{
	case '*':
	case '/':
	weight = 2;
	break;
	case '+':
	case '-':
	weight = 1;
	break;
	}
	return(weight);
	}

view raw InfixtoPostfix.cpp hosted with ❤ by GitHub