Task: Parsing_RPN to infix conversion
C: #include<stdlib.h>
#include<string.h>
#include<stdio.h>

char** components;
int counter = 0;

typedef struct elem{
	char data[10];
	struct elem* left;
	struct elem* right;
}node;

typedef node* tree;

int precedenceCheck(char oper1,char oper2){
	return (oper1==oper2)? 0:(oper1=='^')? 1:(oper2=='^')? 2:(oper1=='/')? 1:(oper2=='/')? 2:(oper1=='*')? 1:(oper2=='*')? 2:(oper1=='+')? 1:(oper2=='+')? 2:(oper1=='-')? 1:2;
}

int isOperator(char c){
	return (c=='+'||c=='-'||c=='*'||c=='/'||c=='^');
}

void inorder(tree t){
	if(t!=NULL){
		if(t->left!=NULL && isOperator(t->left->data[0])==1 && (precedenceCheck(t->data[0],t->left->data[0])==1 || (precedenceCheck(t->data[0],t->left->data[0])==0 && t->data[0]=='^'))){
			printf("(");
			inorder(t->left);
			printf(")");
		}
		else
			inorder(t->left);
	
		printf(" %s ",t->data);
	
		if(t->right!=NULL && isOperator(t->right->data[0])==1 && (precedenceCheck(t->data[0],t->right->data[0])==1 || (precedenceCheck(t->data[0],t->right->data[0])==0 && t->data[0]!='^'))){
			printf("(");
			inorder(t->right);
			printf(")");
		}
		else
			inorder(t->right);
	}
}

char* getNextString(){
	if(counter<0){
		printf("\nInvalid RPN !");
		exit(0);
	}
	return components[counter--];
}

tree buildTree(char* obj,char* trace){
	tree t = (tree)malloc(sizeof(node));
	
	strcpy(t->data,obj);
	
	t->right = (isOperator(obj[0])==1)?buildTree(getNextString(),trace):NULL;
	t->left = (isOperator(obj[0])==1)?buildTree(getNextString(),trace):NULL;
	
	if(trace!=NULL){
			printf("\n");
			inorder(t);
	}

	return t;
}

int checkRPN(){
	int i, operSum = 0, numberSum = 0;
	
	if(isOperator(components[counter][0])==0)
		return 0;
	
	for(i=0;i<=counter;i++)
		(isOperator(components[i][0])==1)?operSum++:numberSum++;

	return (numberSum - operSum == 1);
}

void buildStack(char* str){
	int i;
	char* token;
	
	for(i=0;str[i]!=00;i++)
		if(str[i]==' ')
			counter++;
		
	components = (char**)malloc((counter + 1)*sizeof(char*));
	
	token = strtok(str," ");
	
	i = 0;
	
	while(token!=NULL){
		components[i] = (char*)malloc(strlen(token)*sizeof(char));
		strcpy(components[i],token);
		token = strtok(NULL," ");
		i++;
	}
}

int main(int argC,char* argV[]){
	int i;
	tree t;
	
	if(argC==1)
		printf("Usage : %s <RPN expression enclosed by quotes> <optional parameter to trace the build process>",argV[0]);
	else{
		buildStack(argV[1]);
		
		if(checkRPN()==0){
			printf("\nInvalid RPN !");
			return 0;
		}
		
		t = buildTree(getNextString(),argV[2]);
		
		printf("\nFinal infix expression : ");
		inorder(t);
	}
	
	return 0;
}

VB: Option Strict On

Imports System.Text.RegularExpressions

Module Module1

    Class Operator_
        Sub New(t As Char, p As Integer, Optional i As Boolean = False)
            Token = t
            Precedence = p
            IsRightAssociative = i
        End Sub

        Property Token As Char
            Get
                Return m_token
            End Get
            Private Set(value As Char)
                m_token = value
            End Set
        End Property

        Property Precedence As Integer
            Get
                Return m_precedence
            End Get
            Private Set(value As Integer)
                m_precedence = value
            End Set
        End Property

        Property IsRightAssociative As Boolean
            Get
                Return m_right
            End Get
            Private Set(value As Boolean)
                m_right = value
            End Set
        End Property

        Private m_token As Char
        Private m_precedence As Integer
        Private m_right As Boolean
    End Class

    ReadOnly operators As New Dictionary(Of Char, Operator_) From {
        {"+"c, New Operator_("+"c, 2)},
        {"-"c, New Operator_("-"c, 2)},
        {"/"c, New Operator_("/"c, 3)},
        {"*"c, New Operator_("*"c, 3)},
        {"^"c, New Operator_("^"c, 4, True)}
    }

    Class Expression
        Public Sub New(e As String)
            Ex = e
        End Sub

        Sub New(e1 As String, e2 As String, o As Operator_)
            Ex = String.Format("{0} {1} {2}", e1, o.Token, e2)
            Op = o
        End Sub

        ReadOnly Property Ex As String
        ReadOnly Property Op As Operator_
    End Class

    Function PostfixToInfix(postfix As String) As String
        Dim stack As New Stack(Of Expression)

        For Each token As String In Regex.Split(postfix, "\s+")
            Dim c = token(0)
            Dim op = operators.FirstOrDefault(Function(kv) kv.Key = c).Value
            If Not IsNothing(op) AndAlso token.Length = 1 Then
                Dim rhs = stack.Pop()
                Dim lhs = stack.Pop()

                Dim opPrec = op.Precedence

                Dim lhsPrec = If(IsNothing(lhs.Op), Integer.MaxValue, lhs.Op.Precedence)
                Dim rhsPrec = If(IsNothing(rhs.Op), Integer.MaxValue, rhs.Op.Precedence)

                Dim newLhs As String
                If lhsPrec < opPrec OrElse (lhsPrec = opPrec AndAlso c = "^") Then
                    
                    newLhs = "(" + lhs.Ex + ")"
                Else
                    newLhs = lhs.Ex
                End If

                Dim newRhs As String
                If rhsPrec < opPrec OrElse (rhsPrec = opPrec AndAlso c <> "^") Then
                    
                    newRhs = "(" + rhs.Ex + ")"
                Else
                    newRhs = rhs.Ex
                End If

                stack.Push(New Expression(newLhs, newRhs, op))
            Else
                stack.Push(New Expression(token))
            End If

            
            Console.WriteLine("{0} -> [{1}]", token, String.Join(", ", stack.Reverse().Select(Function(e) e.Ex)))
        Next

        Return stack.Peek().Ex
    End Function

    Sub Main()
        Dim inputs = {"3 4 2 * 1 5 - 2 3 ^ ^ / +", "1 2 + 3 4 + ^ 5 6 + ^"}
        For Each e In inputs
            Console.WriteLine("Postfix : {0}", e)
            Console.WriteLine("Infix : {0}", PostfixToInfix(e))
            Console.WriteLine()
        Next
        Console.ReadLine() 
    End Sub

End Module