Using the code below (assuming that all funtions and objects have been defined)

Question

Using the code below (assuming that all funtions and objects have been defined) fill in the calculate postfix funtion.

#include <iostream>
#include <cmath>
#include <cstring>
#include "GenericList.cc"
#include "Queue.cc"
#include "Stack.cc"
using namespace std;

Queue<char> Convert(Queue<char>&);
double Calculate(Queue<char>&);
bool IsOperand(char);
int InfixPriority(char);
int StackPriority(char);

int main()
{
   char line[256];

   while (cin.getline(line, 256))
   {
       Queue<char> infix;
       Queue<char> postfix;

       for (int i=0; i<strlen(line); i++)
           infix.Enqueue(line[i]);
       cout << infix << endl;
       postfix = Convert(infix);
       cout << postfix << endl;
       cout << Calculate(postfix) << endl << endl;
   }

   return 0;
}

Queue<char> Convert(Queue<char>& infix)
{
    Queue<char> postfix;
    Stack<char> oper;
    while(!infix.IsEmpty())
    {

        char t= infix.Peek();
        infix.Dequeue();

        if(IsOperand(t))
        {
            postfix.Enqueue((t));
        }
        else if(oper.IsEmpty())
        {
            oper.Push(t);
        }
        else if(t=='(')
        {
            oper.Push(t);
        }
        else if(t==')')
        {
            while(oper.Peek()!= '(')
            {
                postfix.Enqueue(oper.Peek());
                oper.Pop();
            }
            oper.Pop();
        }
        else
        {
            while(!oper.IsEmpty() && oper.Peek()!= '(' && InfixPriority(t)<= StackPriority(oper.Peek()))
            {
                postfix.Enqueue(oper.Peek());
                oper.Pop();
            }
            oper.Push(t);
        }
    }
    while (!oper.IsEmpty())
    {
        postfix.Enqueue(oper.Peek());
        oper.Pop();
    }
    return postfix;
}

double Calculate(Queue<char>& postfix)
{
   Stack<double> S;
  
   while(!postfix.IsEmpty())
    {
      
    }
  
   return S.Pop();
}

bool IsOperand(char c)
{
   return (c >= '0' && c <= '9');
}

int InfixPriority(char c)
{
   switch (c)
   {
       case '(':
           return 4;
       case '^':
           return 3;
       case '*':
       case '/':
           return 2;
       case '+':
       case '-':
           return 1;
       default:
           return 0;
   }
}

int StackPriority(char c)
{
   switch (c)
   {
       case '^':
       case '*':
       case '/':
           return 2;
       case '+':
       case '-':
           return 1;
       default:
           return 0;
   }
}

okay so this code works it should print out e.g.

5+7

57+

12   i have it printing out 5+7 and 57+ but i cannot get it to calculate the expression.

ps this should work for amore complex single digit expressions such as 2^2^2

thank you

Explanation / Answer

# include <iostream>
# include <cstring>

using namespace std;

struct node
{
char data;
node *next;
};

node *top=NULL;
node *bottom=NULL;
node *entry;
node *endentry;
node *secondendentry;

void push(const char Element)
{
entry=new node;
if(bottom==NULL) {
entry->data=Element;
entry->next=NULL;
bottom=entry;
top=entry;
}
else
{
entry->data=Element;
entry->next=NULL;
top->next=entry;
top=entry;
}
}

const char pop( ) {
char Element=NULL;

if(bottom==NULL)
cout<<" Stack is empty. "<<endl;

else {
for (endentry=bottom; endentry->next!=NULL; endentry=endentry->next)
secondendentry=endentry;

if(top==bottom)
bottom=NULL;

Element=top->data;

delete top;

top=secondendentry;
top->next=NULL;
}

return Element ;
}

void infix_to_postfix(const char *Infix) {
char Infix_expression[100]={NULL};
char Postfix_expression[100]={NULL};

strcpy(Infix_expression,"(");
strcat(Infix_expression,Infix);
strcat(Infix_expression,")");

char Element[5]={NULL};
char Temp[5]={NULL};

for(int count=0;count<strlen(Infix_expression);count++) {
Element[0]=Infix_expression[count];

if(Element[0]=='(')
push(Element[0]);

else if(Element[0]==')') {
Element[0]=pop( );

while(Element[0]!='(')
{
strcat(Postfix_expression,Element);

Element[0]=pop( );
}
}

else if(Element[0]=='^' || Element[0]=='*' || Element[0]=='/'
|| Element[0]=='+' || Element[0]=='-')
{
if(Element[0]=='*' || Element[0]=='/')
{
Temp[0]=pop( );

while(Temp[0]=='^' || Temp[0]=='*' || Temp[0]=='/')
{
strcat(Postfix_expression,Temp);

Temp[0]=pop( );
}

push(Temp[0]);
}

else if(Element[0]=='+' || Element[0]=='-')
{
Temp[0]=pop( );

while(Temp[0]!='(')
{
strcat(Postfix_expression,Temp);

Temp[0]=pop( );
}

push(Temp[0]);
}

push(Element[0]);
}

else
strcat(Postfix_expression,Element);
}

cout<<" Postfix Expression : "<<Postfix_expression;
}

int main( ) {
char Infix_expression[100]={NULL};
cout<<" Enter the Infix Expression : ";
cin>>Infix_expression;
infix_to_postfix(Infix_expression);
return 0;
}

Related Questions

Navigate

• Browse (All)
• Browse U
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.