Q1: Is tmp assigned to the values of the number and operator from buf? 
Q2: Why does my program exit, if I input "3+"?
Q3: Where do you check for the extra spacing? 


Q1: Is tmp assigned to the values of the number and operator from buf? 
A1: NO, "tmp" is only assigned the number.  
    Remember to put a '\0' at the end of your tmp[] before atof()
    "op" is assigned the operator.


Q2: Why does my program exit, if I input "3+"?
A2: The input will always have a space between the operand and operator.


Q3: Where do you check for the extra spacing? 
A3:
1) Look at the sample input.  Two places have extra spacing.
  a) Before the number 
  b) Before the operator
  Therefore place the given while loop skipping spaces in those 2 locations.
2) NOTE:  Do **NOT** check for a specific 'A' or 'B'!!!  The "isdigit()" 
should be doing this.  Do not "hardcode" an 'A' into your source code.
3) Therefore the BIG picture. "[]" optional
Legal Input:        whitespace Real_number whitespace Operator
Legal Operator:     + - * / = q Q
Legal Real_number:  [minus]  number  [.] [number]
               or   [minus] [number]  .  [number]