Chapter 18, Problem 15PC

Program Plan Intro

Stack Based evaluation of prefix expression

Program Plan:

• Declare a structure to create a stack element.
  • Include all the required header files.
• Declare a function to input prefix statements.
• Declare a Function int evaluate that evaluates the prefix expression by considering if the next token in the input stream is an integer, read  the integer and push it onto the stack using the push() operation of the stack .
  • But if the input stream is an operator, pop the last two values from the stack using the pop operation and apply the operator, and push the result onto the stack and the lone value is the result.
• Declare the function bool prefix_reducible that returns true if there are at least three elements on the stack and top two elements are values and the third from the top is an operator.
• Declare the main function.
  • Prompt the user to enter a prefix expression.
    • Evaluate the prefix expression by calling the int evaluate function and print the result.