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My BASIC Notes

DEF
Abbreviation: D <SHIFT+E>

TYPE: Statement
FORMAT: DEF FN <name> ( <variable> ) = <expression>

Action: This sets up a user-defined function that can be used later in the program. The function can consist of any mathematical formula. User defined functions save space in programs where a long formula is used in several places. The formula need only be specified once, in the definition statement, and then it is abbreviated as a function name. It must be executed once, but any subsequent executions are ignored.

The function name is the letters FN followed by any variable name. This can be 1 or 2 characters, the first being a letter and the second a letter or digit.

EXAMPLES of DEF FN Statement:

10 DEF FN A(X)=X+7
20 DEF FN AA(X)=Y*Z
30 DEF FN A9(Q) = INT(RND(1)*Q+1)

The function is called later in the program by using the function name with a variable in parentheses. This function name is used like any other variable, and its value is automatically calculated,

EXAMPLES of FN Use:

40 PRINT FN A(9)
50 R=FN AA(9)
60 G=G+FN A9(10)

In line 50 above, the number 9 inside the parentheses does not affect the outcome of the function, because the function definition in line 20 doesn't use the variable in the parentheses. The result is Y times Z, regardless of the value of X. In the other two functions, the value in parentheses does affect the result.