## Appendix D – The Calculator The ZX Spectrum Next can be used as a full function calculator. ### Selecting the calculator To use the calculator, call up the *Startup Menu* with **EDIT** and select the *Calculator* option. (If you don't know how to select a menu option, refer back to *Quick Start.)* The calculator may be selected as soon as the ZX Spectrum Next is switched on. Alternatively, if you are working on a *NextBASIC* program, you may select the calculator by choosing the *Exit* option from the *Edit/Options Menu* (which returns you to the *Startup Menu*), at which point you can select the *Calculator* option. Note that any *NextBASIC* program which was being worked on (when you selected the calculator) will be remembered and restored when you exit from the calculator and return to *NextBASIC*. ### Entering numbers When you have selected the *Calculator* option, the screen will change to:  ``` Calculator ``` *Fig. 54 – Calculator Screen* and the ZX Spectrum Next's calculator is ready to accept your first entry. Type in: ``` 6+4 ``` As soon as you press **ENTER**, the answer **10** will appear on the next line. (Note that you don't type = as you would on a conventional calculator.) ### Running total You will see that the cursor is positioned to the right of the answer, which is a *running total* (like on a conventional calculator). This means that you can simply type in the next operation to be carried out on the running total (without having to type in a whole new calculation). So, with the cursor still positioned to the right of the **10** on the screen, type in: ``` /5 ``` and the answer **2** appears. ### Using built-in mathematical functions The ZX Spectrum Next's calculator leverages the power of *NextBASIC* to provide more advanced functions to the user. For example, with the result of the previous operation in place, type in: ``` *PI ``` This produces the result **6.2831853** on the screen. The ZX Spectrum Next has used its built-in π function – all you had to do was type in **PI**. This applies to all the ZX Spectrum Next's mathematical functions. To demonstrate, type in: ``` *ATN 60 ``` which will give you the result **9.7648943**. ### Editing the screen To further enhance the calculator's flexibility, you may also edit the contents of the screen. To demonstrate, move the cursor (using the cursor left key) to the beginning of the line and then type in **INT** so that the line reads ``` INT 9.7648943 ``` and as soon as **ENTER** is pressed, the answer **9** will appear. This also demonstrates that the ZX Spectrum Next doesn't have to perform a calculation in order to print the value of an expression. As another example, press **ENTER** and type: ``` 1E6 ``` which will return the value of that expression. Notice that before you typed in **1E6**, you pressed **ENTER** on its own – this tells the ZX Spectrum Next that you are about to start a new calculation. ### Assigning variables One extremely useful feature of the ZX Spectrum Next's calculator is that it allows you to assign values to variables and then use them in subsequent calculations. This is achieved by using the **LET** statement (unlike *NextBASIC* the Calculator doesn't yet allow assignments without **LET**). To demonstrate, press **ENTER** and type in the following: ``` LET x=10 ``` You must then press **ENTER** twice for the ZX Spectrum Next to accept the variable assignment. Now verify that the variable **x** is being used, by typing: ``` x+90 ``` then ``` +x*x ``` If you are using the calculator whilst working on a *NextBASIC* program, then any variables used by the calculator should be chosen so that they do not conflict with those used by the program itself. Note that *NextBASIC* keywords are not allowed to be used as variable names. ### User defined functions Note that if you have set up any user defined functions (using the **DEF FN** statement) whilst working on a *NextBASIC* program, you will be able to invoke that function when using the calculator. To illustrate this point, return to *NextBASIC* and type in (for example): ``` 9000 DEF FN c(n)=n*n*n ``` which sets up the user defined function **FN c(n)** which returns the *cube* of *n* (the number you type into the parentheses). Now exit from *NextBASIC* and return to the calculator – you can now use this user defined function as if it were one of the ZX Spectrum Next's own built-in functions. For example, enter: ``` FN c(3) ``` and the calculator will print the number **27** (i.e. the *cube of 3*). ### Exiting from the calculator When you have finished using the calculator, press the **EDIT** key. The screen will change to:  ``` Options < 14MHz Calculator 32/64/85 Exit 1792K Calculator ``` *Fig. 55 – Calculator Options Menu* Select the *Exit* option to return to the opening menu. If you were working on a *NextBASIC* program before you started using the calculator, then you may return to the program by selecting the *NextBASIC* option. (If you wish to continue using the calculator, then select the *Calculator* option).