| layout | sheet |
|---|---|
| title | BASIC-DOS BASIC Commands |
| permalink | /docs/bdman/cmd/basic/def/ |
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The DEF statement defines single-line functions ("function expressions"):
DEF name[(parameter[,parameter]...)]=expression
The DEF statement can also define multi-line functions ("function blocks"), but only from within a BASIC program:
DEF name[(parameter[,parameter]...)]
statement(s)
RETURN expression
Function and parameter names follow the same rules as variable names, so a name ending with $ defines a string function or parameter, and a name ending with % defines an integer function or parameter.
Example:
LET PI = 3.141593
DEF AREA(R) = PI * R^2
PRINT "Area is "; AREA(2)
Area is 12.566372
Example (in a BAS file):
DEF HYP(A,B)
LET C = A*A + B*B
RETURN SQR(C)
PRINT HYP(3,4); C
5 25
A function block ends with its first RETURN statement, so RETURN can't be used conditionally (eg, IF N < 0 THEN RETURN 0). Parameters can't be assigned new values, and any other variables used in a function block are shared with the rest of the program (like C above).
Like variables, functions defined within a BASIC program remain defined after the program ends and can be used in commands typed at the prompt:
PRINT "Area is "; AREA(3)
Area is 28.274337
The DEF SEG statement is unrelated; it sets the segment used by PEEK and POKE.
BASIC-DOS does not require function names to begin with the letters FN, it allows single-line functions to be defined immediately (in "Direct Mode"), and it allows multi-line functions.
Note that DEF FN X=... (with a space after FN) is not the same as DEF FNX=...: BASIC-DOS treats it as the start of a function block, which then swallows the rest of the program.
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