CS 456 - Systems Programming Spring 2024

Displaying ./code/apr17/rpn.c

// rpn.c: reverse polish notation calculator

#include "rpn.h"

int main(void) {

  //get variable declarations
  int  type;             //type of input
  char input[MAXOPSIZE]; //stores the input
  double op2;            //stores a number

  while ( (type = getop(input, MAXOPSIZE)) != EOF ) {
    
    switch ( type ) {
    case NUMBER:           //we get a number
      push(atof(input));   // convert number to an integer, push it onto the stack
      break;
    case '+':
      push(pop() + pop()); // pop the two numbers from the stack and add them
      break;
    case '*':
      push(pop() * pop()); // pop the top two numbers from the stack and multiply them
      break;
    case '-':
      op2 = pop();         //pop number on top of the stack, stores it in op2 
      push(pop() - op2);   //pop next number, subtract op2 from that number, push that to top stack
      break;
    case '/':
      op2 = pop();  // pop top of stack, store in op2
      if ( op2 == 0.0 )    // check if this is Zero, as we dont want a divide by Zero error
        printf("Divide by zero.\n");
      else
        push(pop() / op2);  // pop next number, divide it by op2
      break;
    case '=': 
      printf("Top: %f\n", push(pop()));  // essentally taking what's on top of the stack, printing it, then pushing it back
      break;
    case 'c':
      clear_stack(); //clears the stack
      break;
    case TOOBIG:
      printf("Input too large: '%s'\n", input); // input is too large
      break;
    default:
      printf("Unknown command: '%c'\n", type); //unknown command entered
    }
  }
   // end while

  return 0;
}