Functions are similar to procedures, but they have only one purpose - to give a single result. The easiest way to understand a function is to describe some of the computer's own. It has logs - the trigonometric functions such as SIN, TAN and COS. One of the most useful functions is RND, which supplies random numbers. It is usually used with a parameter, and gives a random integer between 1 and the value of the parameter. So RND(50) will pick a random number between and possibly including 1 and 50. When you type X=RND(4), you know that the result of the function RND will be placed in X. The RND function is described in more detail in chapter 25.

A function can be used with any number of parameters, both string and numeric. Here is a function to determine the mass of a sphere:

Here's another example of using a function in a program

Line 5 clears the screen, and lines 20 to 50 print instructions on the screen.

Line 60 prints a request for you to enter an amount, waits for you to do so, and puts the value into variable Y.

Line 70 prints a message, and calls a function called FN_discount(Y). The value in Y is passed to the function's parameter (which is the 'actual' parameter).

Line 100 starts the definition of the function, and passes the parameter value to a 'formal' parameter called SUM.

Line 110 contains a conditional statement. If the value of SUM is 100 or less, then the function returns the result given by SUM-(20*SUM/100). If the value of SUM is more than 100, then the execution of line 110 stops before working out the SUM-(20*SUM/100), and line 120 has a go - and so son.

Notice the underline character in FN_discount. This helps to make the function's name more readable.