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Prefix Functions and Precedence

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Prefix Functions

Traditionally, in non-RPN Calculators, functions were entered after the expression - so when in Mathematics you would write "sin 2.5" on a calculator you would press 2.5 then press Sin Button.

Thus software calculators started out this way as well.

However many modern physical calculators allow you to enter your formulae the same way you write it mathematically. So if the function occurs first then you press it first. So in the above you press Sin Button then 2.5. We refer to this as having Prefix Functions On.

Prefix Functions can be turned off - see Optons.


Sqrt 2

  Prefix On:  Square Root Button then 2

  Prefix Off:  2 then Square Root Button

log 4.5

  Prefix On:  Log Button then 4.5

  Prefix Off:  4.5 then Log Button


  Prefix On and Prefix Off:  5 then Square Button (as this is not a function that is written in Prefix mode)


  Prefix On and Prefix Off:  7 then Power Button then 2.5 (as this is not a function that is written in Prefix mode)


According to standard arithmetic, multiplication and division have precedence over addition and subtraction - this means they are done first.

So 2 + 3 x 4 means that the calculator works out the multiplication first, then the addition. So this evaluates to 14, NOT 20!

If you want the addition to evaluate first, then you need to use brackets:

( 2 + 3 ) x 4 = 20

To implement this, the calculator maintains a stack of values (operands) and a stack of operators.

Normal Precedence can be turned off in the Options.

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Last Updated: 8:28am 25th January 2023

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