C++ Program For Infix to Postfix Expression Converter

Problem:- An infix expression is the usual way we write expressions. In infix expression, operators are written in-between their operands. For example, A * ( B + C ) / D is an infix expression. In postfix expression, operators are written after their operands. The infix expression given above is equivalent to A B C + * D /. Good Reference Article: C++ Even or Odd Program

Logic:- This program makes use of the stack. A stack is used to store elements in LIFO order. The element which comes at the end is deleted first. You can imagine that MS Word uses a stack to store operation in a specific order. When we perform ‘undo’ then it deletes the last operation performed.

This program takes a string of an infix expression and gives a string of postfix operation. It simply considers the every character of the infix string and if the character being considered is a number then it is appended to the postfix string. If it is a symbol then it is pushed onto the stack. Rest of the process is quite simple. The code is also self-explanatory.

Solution:-

#include<iostream>

#include<cstring>

using namespace std;

class stack

{

  private:

  

   int arr[5];

   int top;

   int size;

public:

  

   stack()

   {

     top=-1;

     size=5;

   }

   bool IsEmpty()

   {

     if(top==-1)

     {

      return true;

     }

     else

     {

      return false;

     }

   }

bool IsFull()

{

    if(top==size-1)

    {

     return true;

    }

    else

    {

     return false;

    }

}

void push(int data)

{

    if(IsFull())

    {

     cout<<"STACK IS FULL..."<<endl;

    }

    else

    {

     top++;

     arr[top]=data;

    }

}

int pop()

{

    if(IsEmpty())

    {

     cout<<"STACK IS EMPTY..."<<endl;

    }

    else

    {

     int c;

     c=arr[top];

     top--;

     return c;

    }

}

void show()

{

    if(IsEmpty())

    {

     cout<<"STACK IS EMPTY..."<<endl;

    }

    else

    {

     for (int i=0;i<=top;i++)

     {

       cout<<"DATA ---- "<<arr[i]<<endl;

     }

    }

}

int getweight(char ch)

{

    switch(ch)

    {

     case '/':

     case '*': return 2;

     case '+':

     case '-': return 1;

     default: return 0;

    }

}

void in2p(char in[],char po[],int size)

{

    int i=0,k=0;

    int w;

    char ch;

    

 while(i<size)

    {

     ch=in[i];

     w=getweight(ch);

     

  if(w==0)

     {

       po[k++]=ch;

     }

     else

     {

       if(IsEmpty())

       {

         push(ch);

       }

    

       else

       {

         while(!IsEmpty() && w<=getweight(arr[top]))

         {

           po[k++]=arr[top];

           pop();

         }

         push(ch);

       }

     }

     i++;

 }

    while(!IsEmpty())

    {

     po[k]=arr[top];

     k++;

     pop();

    }

    po[k]=0;

}

};

int main()

{

  char given[]="1+2*3";

  int s=strlen(given);

  char desired[s];

  stack obj;

  obj.in2p(given,desired,s);

  cout<<"\n\n\n\t\t----------------------------------------------";

  cout<<"\n\t\t|                                            |";

  cout<<"\n\t\t|   INFIX TO POSTFIX EXPRESSION CONVERTER    |";

  cout<<"\n\t\t|                                            |";

  cout<<"\n\t\t----------------------------------------------\n";

  cout<<"\t\tINFIX EXPRESSION = "<<given; 

  cout<<"\n\n\t\tPOSTFIX EXPRESSION = "<<desired<<endl<<endl;

  system("pause");

};

Output:-

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