How can i scroll the mathematical expression In C++?

Question

I mean I want to ask user to enter a mathematical expression which is postfix and is in an string Like a next scroll the mathematical expression from the end of the string (which contain that mathematical expression) then change this to infix mathematical expression and print out finally . Please help me.

The point in this conversion ( postfix to infix ) try to use less parenthesis  .

 

 

For example:  

  the postfix mathematical expression :    d a b + c * -

 

after change to the infix mathematical expression : d - ( a + b ) * c