Program converts the given infix expression in to postfix form

#include

#include

#include

#include



class expression

{

	private:

		 char infix[100];

		 char stack[200];

		 int top;	

		 int r;

		 char postfix[100];

	public:	

		 void convert();

		 int input_p(char);

		 int stack_p(char);

		 int rank(char);

};



int expression::input_p(char c)

{

	if(c==’+’ || c==’-')

		return 1;

	else if(c==’*’ || c==’/')

 		return 3;

	else if(c==’^')

		return 6;

	else if(isalpha(c)!=0)

		  return 7;

	else if(c==’(')

		return 9;

	else if(c==’)')

		return 0;

	else

	{

		cout<<”Invalid expression ::input error\n”;

		exit(0);

	}

}



int expression::stack_p(char c)

{

	if(c==’+’ || c==’-')

		return 2;

	else if(c==’*’ || c==’/')

		return 4;

	else if(c==’^')

		return 5;

	else if(isalpha(c)!=0)

		return 8;

	else if(c==’(')

		return 0;

	else

 	{

		cout<<”Invalid expression  ::stack error\n”;

		exit(0);

	}

}



int expression::rank(char c)

{

	if(c==’+’ || c==’-')

		return -1;

	else if(c==’*’ || c==’/')

 		return -1;	

	else if(c==’^')

		return -1;

	else if(isalpha(c)!=0)

		return 1;	

	else

	{

		cout<<”Invalid expression ::in rank\n”;

		exit(0);

	 }

}



void expression::convert()

{

 cout<  <<”in to postfix form”;

 cout<<”Enter an infix expression ::\n”;

 cin>>infix;

 int l=strlen(infix);



 infix[l]=’)';

 infix[l+1]=”;



 //Convertion starts

 top=1;

 stack[top]=’(';



 r=0;

 int x=-1;



 int i=0;

 char next=infix[i];



 while(next!=”)

 {

	  //Pop all the elements to outputin stack which have higher precedence

	  while( input_p(next) < stack_p(stack[top]) )

	  {

		if(top<1)

		{

			cout<<”invalid expression ::stack error\n”;

			exit(0);

		}



		postfix[++x]=stack[top];

		top–;



		r=r+rank(postfix[x]);

   

   		if(r<1)

   		{	

			cout<<”Invalid expression  ::r<1\n”;

			exit(0);

   		}

	}



	if(input_p( next ) != stack_p( stack[top]))

		stack[++top]=next;

	else

		top–;



		i++;

		next=infix[i];

 	}

 postfix[++x]=”;



 if(r!=1 || top!=0)

 {

  cout<<”Invalid expression ::error in rank or stack\n”;

  exit(0);

 }



 cout<<”\n\nThe corresponding postfix expression is ::\n”;

 cout<}

int main()

{

 expression obj;

 obj.convert();

 return 0;

}