DSA C25 Program

Group C: (Assignment No: 02) (SPPU Syllabus Assignment No: 25)
Problem Statement:

Implement C++ program for expression conversion as infix to postfix and its evaluation using stack based on given conditions
i. Operands and operator, both must be single character.
ii. Input Postfix expression must be in a desired format.
iii. Only '+', '-', '*' and '/ ' operators are expected.

Program Code:

//================================================================================================================================
// Name        : infix_postfix.cpp
// Author      : Nitin Shivale
// Version     : 1
// Copyright   : Your copyright notice
// Description : Conversion of infix expression to postfix expression and evaluation of postfix expression using stack, Ansi-style
//================================================================================================================================

#include <iostream>
#include<ctype.h>
using namespace std;
//class inpo containing data member and member functions
class inpo
{
    char in[20],po[20],stk[10];//stack for expression conversion.
    int i,j,is,ic,top,top1; //Two top one for stack and one for stack 1.
    int stk1[10]; //Stack 1 for expression evaluation.
public:
    inpo()
    {
     i=j=is=ic=0; //initialization of data members
     top=top1=-1;
    }
    bool IsOperand(char C)
    {
        if(C >= '0' && C <= '9') return true;
        if(C >= 'a' && C <= 'z') return true;
        if(C >= 'A' && C <= 'Z') return true;
        return false;
    }
    void getinfix() //Accept the infix expression
    {
        cout<<"\nEnter valid infix Expression: ";
        cin>>in; //Stored infix exp in in[]char array.
    }
    void showinfix() //Show the infix expression
    {
        cout<<"\t"<<in;
    }
    int isempty() //Stack basic functions.
    {
        if(top==-1)
            return 1;
        else
            return 0;
    }
    int isfull()
    {
        if(top==9)
            return 1;
        else
            return 0;
    }
    void push1(int x1)//for integer stack
    {
        top=top+1;
        stk1[top]=x1;
    }
    int pop1() //for integer stack
    {
       int s1;
       s1=stk1[top];
       top=top-1;
       return s1;
    }
    void push(char x)//for character stack
    {
        top=top+1;
        stk[top]=x;
    }
    char pop()//for character stack
    {
        char s;
        s=stk[top];
        top=top-1;
        return s;
    }
    void showpostfix()
    {
        cout<<"\t"<<po;
    }
    void convert();
    int instackprio();
    int incomingprio(char); //member functions
    void postfixExpEval();
};
void inpo::postfixExpEval() //To evaluate the postfix expression
{
    i=0;
    char ch;
    int op1,op2,res,tot;
        while(po[i]!='\0')//read postfix expression one by one
        {
            ch=po[i];
            if((ch=='+')||(ch=='-')||(ch=='*')||(ch=='/')||(ch=='^')) //isdigit(ch) built in function to check digit.
            {
                switch(ch)//if operator pop and perform operation and push back into the stack.
                {
                case '+':op2=pop1();
                         op1=pop1();
                         res=op1+op2;
                         push1(res);
                         break;
                case '-':op2=pop1();
                         op1=pop1();
                         res=op1-op2;
                         push1(res);
                         break;
                case '*':op2=pop1();
                         op1=pop1();
                         res=op1*op2;
                         push1(res);
                         break;
                case '/':op2=pop1();
                         op1=pop1();
                         res=op1/op2;
                         push1(res);
                         break;
                case '^':op2=pop1();
                         op1=pop1();
                         res=op1;
                         while(op2>1)
                         {
                          res=res*op1;
                          op2--;
                         }
                         push1(res);
                         break;
                }//end of switch

            } //end of if
            else if(IsOperand(ch))//To check operand we use IsOperand function.
            {
                push1(ch-'0'); //if operand push it inside stack
            } //end of else
            i=i+1;
        }//end of while

    tot=pop1(); //final evaluated result at the top of stack.
    cout<<"\nResult is:"<<tot;
}//end of fun

/*******************************************************************
 * Function Name: To convert infix expression to postfix expression.
 * return type: Void
 *******************************************************************/

void inpo::convert()
{
    i=j=0;
    char p,k;
    while(in[i]!='\0')//do until null character not found
    {
     p=in[i];//to read one by one from infix expression
     if((p=='(')||(p=='+')||(p=='-')||(p=='*')||(p=='/')||(p=='^')||(p==')'))
     {
         if(isempty()) //here we are dealing with operator only as per their priority.
         {
             push(p); //if initially stack is empty push
         }
         else if(p==')') //when we encountered with ')' bracket pop from stack until we r not encountered with '(' bracket.
         {
             k=pop();
             while(k!='(') //check the pop element with '(' bracket. if equal stop poping.
             {
                 po[j]=k; //pop and store it inside the postfix expression array po[].
                 j++;     //increment po[] array index by 1.
                 k=pop(); //pop next element
             }
         }
         else
         {
             is=instackprio(); //when we are pushing the operator inside the stack.
             ic=incomingprio(p);// we are always checking their incoming and instack priority.
             if(is>ic)//if instack priority is gretter than incoming priority
             {
              k=pop(); //pop the stack top operator whose priority is bigger than incoming operator from stack.
              po[j]=k;//store it in postfix expression array po[j]
              j++;  //increment j by one.
              push(p);//then push the incoming operator in stack.
             }
             else
             {
                 push(p); //if incoming operator priority is gretter than instack operator priority then
             }            // directly push the incoming operator inside the stack.
         }
     }
     else// if opearnd is their directly store it inside the postfix expression array po[j].
     {
        po[j]=p;
        j++; //increment j by one.
     }
     i=i+1; //read the next character of infix expression for conversion.
    }//end of while loop
    if(in[i]=='\0')//if we encountered with NULL Character of infix expression then
    {
        while(!isempty())//pop the stack containts until stack is not empty and
        {
         k=pop(); //pop from stack
         po[j]=k; //store it inside the postfix expression array po[j].
         j++;  //increment j by one.
        }
    }
 po[j]='\0'; // at the end of the postfix expression store null character to indicate end of the expression.
}

/* * Function to check the instack priority of operator * */
int inpo::instackprio()
{
    char b;
    b=stk[top];
    switch(b)
    {
     case '(':return 0; break;
     case '+':return 2; break;
     case '-':return 2; break;
     case '*':return 4; break;
     case '/':return 4; break;
     case '^':return 5; break;
    }
}
/* * Function to check the priority of incoming operator * */
int inpo::incomingprio(char ch)
{
    switch(ch)
    {
     case '(':return 9; break;
     case '+':return 1; break;
     case '-':return 1; break;
     case '*':return 3; break;
     case '/':return 3; break;
     case '^':return 6; break;
    }
}

int main()
{
    inpo p1;
    p1.getinfix();
    p1.showinfix();
    cout<<"\nAfter conversion from infix to postfix...\n";
    p1.convert();
    p1.showpostfix();
    cout << "\n\n!!!POSTFIX EXPRESSION EVALUATION ARE AS FOLLOWS..!!!" << endl;
    p1.postfixExpEval();
    return 0;
}

/************** OUTPUT***********************************************************
 *
 Enter valid infix Expression: 2^4
    2^4
After conversion from infix to postfix...
    24^

!!!POSTFIX EXPRESSION EVALUATION ARE AS FOLLOWS..!!!

Result is:16

Enter valid infix Expression: (9-1)/(4-2)^2
    (9-1)/(4-2)^2
After conversion from infix to postfix...
    91-42-2^/

!!!POSTFIX EXPRESSION EVALUATION ARE AS FOLLOWS..!!!

Result is:2

[student@localhost SE_Comp_A]$ g++ conv_in_po_eval.cpp
[student@localhost SE_Comp_A]$ ./a.out

Enter valid infix Expression: (8*6)/(4-2)^3
    (8*6)/(4-2)^3
After conversion from infix to postfix...
    86*42-3^/

!!!POSTFIX EXPRESSION EVALUATION ARE AS FOLLOWS..!!!

Result is:6