This method takes one additional keystroke. Notice that the first intermediate result is still the innermost parentheses (7 ⋅ 3). The advantage to working a problem left–to–right is that you don't have to use [ to reposition operands for nomcommutaiive functions ( …and q).

However, the first method (starting with the innermost parentheses) is often preferred because:

„It takes fewer keystrokes.

„It requires fewer registers in the stack.

Note

When using the left–to–rightmethod, be sure that no more than

 

four intermediate numbers (or results) will be needed at one

 

time (the stack can hold no more than four numbers).

 

 

The above example, when solved left–to–right, needed all registers in the stack at one point:

Keys:Display:Description:

4

‘14 ‘ )

7

‘3

_

z

)

›

)

2

…

)

q

)

Saves 4 and 14 as intermediate numbers in the stack.

At this point the stack is full with numbers for this calculation. Intermediate result. Intermediate result. Intermediate result.

Final result.

More Exercises

Practice using RPN by working through the following problems:

Calculate:

(14 + 12) ⋅ (18 – 12) ⎟ (9 – 7) = 78.0000

2–14RPN: The Automatic Memory Stack