The "Input Order" setting controls how DreamCalc interprets your mathematical input. The active input mode
will be shown in the numeric display as MAL, CAL or RPN. It can be changed from the main menu by clicking
**Modes→Input Order** and selecting one of the following:

Prefix Algebraic (MAL)

- The default option and the same as most algebraic calculators in use today.
- In this mode, to enter 'sin(5) + 3 =', you press
[sin] 5 [+] 3 [ENTER].Postfix Algebraic (CAL)

- Like many algebraic calculators prior to the 1990s.
- For example, to enter 'sin(5) + 3 =', you press
5 [sin] [+] 3 [ENTER].Reverse Polish Notation (RPN)

- Non algebraic input preferred by some calculator users.
- For example, to enter 'sin(5) + 3 =', you key in
5 [sin] [ENTER] 3 [+].

Additional information is provided in the sections below.

This is the same notation used by most modern algebraic calculators. In this mode, you enter expressions in the order they are written. Where applicable, most single value functions operate in a prefix fashion, i.e. you enter them prior to keying in the value.

For example, to enter: *sin(5) + 3 =*, you would press:

[sin] 5 [+] 3 [ENTER]

There are, however, some functions where prefix entry would be inconvenient. For this reason, conversions act
in an exclusively postfix fashion, as do the functions: X^{2}, X^{-1}, iPart, fPart, imag and
real. These require you to press the function key *after* the value.

For example, to get just the fractional part of the value 5.39, use:

5.39 [FRACPT]

This will be shown in the Paper Roll as, *"5.39:FRACPT = 0.39"*.

In prefix mode, the **[+/(-)]** key acts primarily as a "soft minus" (-), rather than a sign toggle. It is
used to indicate explicitly that you are entering a negative value, rather than a subtraction operation.

For specialized forms of input, such as keying in negative exponents and complex values, the use of
**[+/(-)]** is mandatory, as demonstrated in the examples below.

**Example:** *Input of negative exponent.*

5 [EEX] [+/(-)] 28[ENTER]Displays: 5E-28

**Example:** *Complex number input.*

5 [;] 3(input 5 + 3i)[+]23 [;] [+/(-)] 2(23 - 2i, use [+/(-)] for negative input)[ENTER]Displays: 28 + 1i

A multiplication will be implicitly assumed where applicable.

For example, keying in:

3 [cos] 45 [ENTER]

will be interpreted as, "*3 × cos(45) =*".

In postfix (or classic) algebraic mode, all single parameter functions operate in a postfix fashion—you always press the function key after the value. Many calculators prior to the 1990s used this mode of input, and it may still be the most natural method for you.

To enter: *sin(5) + 3 =*, you would key in:

5 [sin] [+] 3 [ENTER]

One of the features of using DreamCalc in postfix mode is that you'll see your input expression displayed in "written order" in the numeric display.

Try the following example. Enter:

45 [sin] [acos]

You will immediately see this shown in the numeric display as: *"acos sin 45"*.

Negative values are entered in postfix mode by toggling the sign of the input using the **[+/(-)]**
key.

For example:

5.39 [+/(-)]Displays: -5.39

The key may also be used to toggle the sign of exponent input when using the **[EEX]** key.

In Reverse Polish Notation (RPN) there is no concept of precedence, nor is there any requirement for
parentheses or an equals key. When DreamCalc is in RPN mode, the parentheses keys function as "stack rolls" and
the **[ENTER]** key is used to "enter" values, rather than operating as "equals". RPN is preferred by many
users because it generally requires fewer key strokes than the equivalent algebraic input.

In RPN mode, calculations are performed on a "stack". This is a list of working values—referred to as registers. When RPN mode is enabled, the Paper Roll Window displays the stack (shown below) rather than an algebraic log of calculations. You'll also see the lower three values of the stack (the T, Z, and Y registers) in the numeric display.

09: 0 08: 0 07: 0 06: 0 05: 0 04: 0 03(T): PI 02(Z): 3 01(Y): 47.3 ______________________ X: 47.3The RPN Stack

The X register represents the current on-screen display or input value. When you press **[ENTER]**, you
push the values up the stack. All single parameter functions operate in a postfix fashion on the X register.
Operations involving two values operate between the Y and X registers. Because of this, there is no concept of
precedence.

For example, to add two numbers together, such as *5 + 3*, you would key in:

5 [ENTER] 3 [+]Displays: 8

The result will be written to the X register and shown in the numeric display. The stack will also shift down automatically.

Now consider the calculation of *(3 + 5) × (2 + 4)*. In RPN, this is entered as follows:

3 [ENTER] 5 [+](sum 3 + 5)[ENTER]2 [ENTER] 4 [+](sum 2 + 4)[×](multiplies the two sums)Answer: 48

The size of the stack is configurable from Options Window.

Negative values are entered in RPN mode by toggling the sign of the input using the **[+/(-)]** key.

For example:

5.39 [+/(-)]Displays: -5.39

The key may also be used to toggle the sign of exponent input when using the **[EEX]** key.

See also: Keyboard Input