IBM 5100 Basic Reference Manual page 70

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• After control is passed to a DEF statement without reference to the function, con-
trol goes to the first executable statement following the function definition-
following the DEF statement for single-line functions, and following the FNEND
statement for multiline functions.
• The last executable statement preceding the FNEND statement should be a
RETURN, STOP, CHAIN, or unconditional GOTO to prevent control from
passing to the FNEND statement.
• If a function definition alters the value of a variable that is referenced in the
same statement that calls the function, unpredictable results may occur.
Example
The following examples illustrate the execution of DEF statements:
10 DEF FNA (X)
=
Xt3/2
20 Y = 10
30 Z= FNA(Y)
After execution of statement 30, the variable Z will have the integer value 500.
In the next example, the variable R will have the integer value 72 after execution of
statement 80. When statement 80 is executed, the current value of Y, which is 2, is
substituted for each occurrence of the dummy variable X in the arithmetic expres-
sion of statement 100. Since the function FNC, defined in statement 100, uses the
function FNB in its. definition, the value 2 is substituted for each occurrence of X in
the arithmetic expression of statement 90. The resulting value, 47, is then substituted
for the function reference FNB(X) in statement 100. The current value of Y, which
is 2, is then added to 47, and the resulting value of 49 is substituted for the function
reference FNC(Y) in statement 80. This value is added to 23, and the resulting
value of 72 is assigned to the variable R.
70 LETY
=
2
80 LET R
=
FNC(Y) + 23
90 DEF FNB(X)
=
5*X**2+27
100 DEF FNC(X) .. FNB(X) + X
The following example shows a multiline function definition. When these state-
ments are executed both C and 0 will have a value of 7.
10A = 5
20 B= 2
30 DEF FNA (X,Y)
40 IF X>O GOTO 60
50 RETURN X-V
60 RETURN X+Y
70 FNEND
80 C
=
FNA (A,B)
90 0 = FNA (A,B)
/