CodeChef/InfixtoPostfix.cpp at master · aviraw/CodeChef · GitHub

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#include<iostream>
#include<stack>
using namespace std;

bool isOperator(char c)
{
	if(c=='+' || c=='-' || c=='/' || c=='*' || c=='^')
	{
		return true;
	}
	else
	{
		return false;
	}
}

int precedence( char c)
{
	if(c=='^')
	return 3;
	else if(c=='*' || c=='/')
	return 2;
	else if(c=='+' || c=='-')
	return 1;
	else
	return -1;
}

string InfixtoPostfix(stack<char> s, string infix)
{
	string postfix;
	for(int i=0;i<infix.length();i++)
	{
		if((infix[i] >='a' && infix[i]<='z') || ( infix[i] >='A' && infix[i]<='Z'))
		{
			postfix+=infix[i];
		}
		else if(infix[i]=='(')
		{
			s.push(infix[i]);
		}
		else if(infix[i]==')')
		{
			while((s.top()!='(') && (!s.empty()))
			{
				char temp=s.top();
				postfix+=temp;
				s.pop();
			}
			if(s.top()=='(')
			{
				s.pop();
			}
		}
		else if(isOperator(infix[i]))
		{
			if(s.empty())
			{
				s.push(infix[i]);
			}
			else
			{
				if(precedence(infix[i])>precedence(s.top()))
				{
					s.push(infix[i]);
				}
				else if((precedence(infix[i])==precedence(s.top())) && (infix[i]=='^') )
				{
					s.push(infix[i]);
				}
				else
				{
					while((!s.empty())&&( precedence(infix[i])<=precedence(s.top())))
					{
						postfix+=s.top();
						s.pop();
					}
					s.push(infix[i]);
				}
			}
		}
	}
	while(!s.empty())
	{
		postfix+=s.top();
		s.pop();

	}

	return postfix;
}

int main()
{
	string infix,postfix_exp;
	cout<<"Enter a Infix Expression : "<<endl;
	cin>>infix;
	stack <char> s;
	cout<<"Infix Expression: "<<infix<<endl;
	postfix_exp=InfixtoPostfix(s,infix);
	cout<<endl<<"Postfix Expression: "<<postfix_exp;

	return 0;
}