### 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):