Updated infix_to_postfix.cpp

infix_to_postfix.cpp

@@ -71,4 +71,83 @@ int main()
     infix_to_postfix(exp);
 
     return 0; 
-}
+}
+
+//using stack.h
+#include<iostream>
+using namespace std;
+#include "stack.h"
+
+int precedence(char s)
+{
+  if(s == '^')
+    return 1;
+  else if(s == '*' || s == '/')
+    return 2;
+  else if(s == '+' || s == '-')
+    return 3;
+  else if(s == '(' || s == ')')
+    return 4;
+  else
+    return -1;
+}
+
+void infix_postfix(string exp)
+{
+  Stack <char> s;
+  s.push('N');
+  int l = exp.length();
+  for(int i=0; i<l; i++)
+  {
+    if(exp[i] == '(')
+      s.push(exp[i]);
+    else if((exp[i] >= 'a' && exp[i] <= 'z') || (exp[i] >= 'A' && exp[i] <= 'Z'))
+      cout<<exp[i];
+    else if(exp[i] == ')')
+    {
+      while(s.top_ele() != '(')
+      {
+        char element = s.top_ele();
+        cout<<element;
+        s.pop();
+      }
+    }
+    else
+    {
+      if(s.top_ele() == 0)
+        s.push(exp[i]);
+      else
+      {
+        int p = precedence(exp[i]);
+        if(p < precedence(s.top_ele()))
+          s.push(exp[i]);
+        else
+        {
+          char c = s.top_ele();
+          s.pop();
+          cout<<c;
+          s.push(exp[i]);
+        }
+      }
+    }
+  }
+  while(s.top_ele() != 'N')
+  {
+    char ele = s.top_ele();
+    if(ele != '(')
+      cout<<ele;
+    s.pop();
+  }
+}
+
+int main()
+{
+  string exp;
+  cout<<"Enter expression: ";
+  cin>>exp;
+
+  cout<<"Postfix expression: ";
+  infix_postfix(exp);
+
+  return 0;
+}