Merge pull request #91 from ashish4321/master

adding infix to postfix conversion using stack

Author: piyush6348

.DS_Store

@@ -0,0 +1,70 @@
+#include <iostream>
+#include <string>
+#include <stack>
+using namespace std;
+
+int precedence(char c)
+{
+	if(c=='^')
+	return 3;
+	else if(c=='*' || c=='/')
+	return 2;
+	else if(c=='+' || c=='-')infixtopostfix.c++
+	return 1;
+	else 
+	return -1;
+}
+
+void converttopostfix(string s)
+{
+	stack<char> st;
+	st.push('N');
+	int l=s.length();
+	string ns;
+	for(int i=0;i<l;i++)
+	{
+		if((s[i] >= 'a' && s[i] <= 'z') || (s[i] >= 'A' && s[i] <= 'Z'))
+		ns=ns+s[i];
+		else if(s[i] == '(')
+		st.push('(');
+		else if(s[i] == ')')
+		{
+			while(st.top() != 'N' && st.top() != '(')
+			{
+				char c=st.top();
+				st.pop();
+				ns=ns+c;
+			}
+			if(st.top() == '(')
+			{
+				char c=st.top();
+				st.pop();
+			}
+		}
+		else
+		{
+			while(st.top() != 'N' && (precedence(s[i])<=precedence(st.top())))
+			{
+				char c=st.top();
+				st.pop();
+				ns=ns+c;
+			}
+			st.push(s[i]);
+		}
+	}
+	while(st.top() != 'N')
+	{
+		char c=st.top();
+		st.pop();
+		ns=ns+c;
+	}
+	
+	cout<<ns<<endl;
+}
+
+int main()
+{		string s;
+		cin>>s;
+		converttopostfix(s);
+	return 0;
+}