From 1a69528ce41de535f2fdcb521cf40ce9b40562a9 Mon Sep 17 00:00:00 2001
From: Amal Ramesh <44441397+amalrhk@users.noreply.github.com>
Date: Wed, 23 Oct 2019 00:00:46 +0530
Subject: [PATCH] Create Infix to Postfix

A program to convert infix to postfix using stack
---
 CPP/InfixToPostfix.cpp | 87 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 CPP/InfixToPostfix.cpp

diff --git a/CPP/InfixToPostfix.cpp b/CPP/InfixToPostfix.cpp
new file mode 100644
index 0000000..dec6cdb
--- /dev/null
+++ b/CPP/InfixToPostfix.cpp
@@ -0,0 +1,87 @@
+/* C++ implementation to convert infix expression to postfix*/
+ 
+#include<bits/stdc++.h> 
+using namespace std; 
+
+//Function to return precedence of operators 
+int prec(char c) 
+{ 
+	if(c == '^') 
+	return 3; 
+	else if(c == '*' || c == '/') 
+	return 2; 
+	else if(c == '+' || c == '-') 
+	return 1; 
+	else
+	return -1; 
+} 
+
+// The main function to convert infix expression 
+//to postfix expression 
+void infixToPostfix(string s) 
+{ 
+	std::stack<char> st; 
+	st.push('N'); 
+	int l = s.length(); 
+	string ns; 
+	for(int i = 0; i < l; i++) 
+	{ 
+		// If the scanned character is an operand, add it to output string. 
+		if((s[i] >= 'a' && s[i] <= 'z')||(s[i] >= 'A' && s[i] <= 'Z')) 
+		ns+=s[i]; 
+
+		// If the scanned character is an ‘(‘, push it to the stack. 
+		else if(s[i] == '(') 
+		
+		st.push('('); 
+		
+		// If the scanned character is an ‘)’, pop and to output string from the stack 
+		// until an ‘(‘ is encountered. 
+		else if(s[i] == ')') 
+		{ 
+			while(st.top() != 'N' && st.top() != '(') 
+			{ 
+				char c = st.top(); 
+				st.pop(); 
+			ns += c; 
+			} 
+			if(st.top() == '(') 
+			{ 
+				char c = st.top(); 
+				st.pop(); 
+			} 
+		} 
+		
+		//If an operator is scanned 
+		else{ 
+			while(st.top() != 'N' && prec(s[i]) <= prec(st.top())) 
+			{ 
+				char c = st.top(); 
+				st.pop(); 
+				ns += c; 
+			} 
+			st.push(s[i]); 
+		} 
+
+	} 
+	//Pop all the remaining elements from the stack 
+	while(st.top() != 'N') 
+	{ 
+		char c = st.top(); 
+		st.pop(); 
+		ns += c; 
+	} 
+	
+	cout << ns << endl; 
+
+} 
+
+//Driver program to test above functions 
+int main() 
+  
+{ 	string exp;
+  	cin>>exp;
+	infixToPostfix(exp); 
+	return 0; 
+} 
+