added d27 code

assignment-27.cpp

@@ -0,0 +1,111 @@
+#include<iostream>
+#include<ctype.h>
+using namespace std;
+
+class stack
+{
+    int top;
+    char data[20];
+    public:
+    stack()
+    {
+        top=-1;
+    }
+
+    void  conversion(char infix[20],char postfix[20])
+    {
+         int j=0,i;
+         char e,token,x;
+         for(i=0;infix[i]!='\0';i++)
+         {
+             token=infix[i];
+             if(isalnum(token))
+             {
+                 postfix[j]=token;
+                 j++;
+             }
+             else
+             {
+                 if(token=='(')
+                     push(token);
+                 else if(token==')')
+                 {
+                     while((x=pop())!='(')
+                     {
+                         postfix[j]=x;
+                         j++;
+                     }
+                 }
+                 else
+                 {
+                     e=topmost();
+                     while(precedence(token)<=precedence(e) && !empty())
+                     {
+                         x=pop();
+                         postfix[j]=x;
+                         j++;
+                     }
+                     push(token);
+                 }
+             }
+         }
+         while(!empty())
+         {
+             x=pop();
+             postfix[j]=x;
+             j++;
+         }
+         postfix[j]='\0';
+    }
+
+    void push(int x)
+    {
+        top++;
+        data[top]=x;
+    }
+
+    int pop()
+    {
+        char x;
+        x=data[top];
+        top--;
+        return x;
+    }
+
+    char topmost()
+    {
+        char e;
+        e=data[top];
+        return e;
+    }
+
+    int precedence(char x)
+    {
+        if(x=='(')
+            return 0;
+        if(x=='+'|| x=='-')
+            return 1;
+        if(x=='*'|| x=='/' ||x=='%')
+            return 2;
+        else
+            return 3;
+    }
+
+    int empty()
+    {
+        if(top==-1)
+            return 1;
+        else
+            return 0;
+    }
+};
+int main()
+{
+    stack s;
+    char infix[20],postfix[20];
+    cout<<"Enter the infix expression: ";
+    cin>>infix;
+    s.conversion(infix,postfix);
+    cout<<"Post fix expression is:  "<<postfix;
+    return 0;
+}