RandomPrograms/infix to postfix.cpp at main · clouds440/RandomPrograms · GitHub

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

int priority (char alpha){
	if (alpha == '+' || alpha == '-'){
		return 1;
	}

	if (alpha == '*' || alpha == '/'){
		return 2;
	}

	if (alpha == '^'){
		return 3;
	}

	return 0;
}

string convert(string infix){
	int i = 0;
	string postfix = "";
	stack<int>s;

	while (infix[i] != '\0'){

		if (infix[i] >= 'a' && infix[i] <= 'z' || infix[i] >= 'A' && infix[i] <= 'Z')
		{
			postfix += infix[i];
			i++;
		}

		else if (infix[i] == '(')
		{
			s.push(infix[i]);
			i++;
		}

		else if (infix[i] == ')')
		{
			while(s.top() != '(')
			{
			postfix += s.top();
			s.pop();
			}

			s.pop();
			i++;
		}

		else
		{
			while (!s.empty() && priority(infix[i]) <= priority(s.top()))
			{
				postfix += s.top();
				s.pop();
			}
			s.push(infix[i]);
			i++;
		}
	}

	while (!s.empty() && s.top() != '(')
	{
		postfix += s.top();
		s.pop();
	}
	return postfix;
}

int main()
{
	string infix, postfix;

	cout << "Enter infix expression: ";
	cin >> infix;

	postfix = convert(infix);
	cout << "Postfix is: " << postfix;

	return 0;
}