DEF Statement ☆☆☆
DEF statements enables us to write functions defined by complicated expressions simply as f(x), g(x,y) and so on.
10 DEF f(x,y)=x^2+3*y^2 20 FOR x=-4 TO 4 30 FOR y=-4 TO 4 40 PRINT x,y,f(x,y) 50 NEXT y 60 NEXT x 70 END
Variables written in the parentheses succeeding DEF are called parameters.
Any variable which is written in other than the DEF line is a different variable, that is, even if it have the same name as that of a parameter, they have distinct locations on the memory.
10 DEF f(x)=x^3 20 LET x=4 30 PRINT f(2) 40 PRINT x 50 END
Variables x in line 10 and x in line 40 are different.
Thus the PRINT statement in line 40 outputs 4.
Variables in Common
Any variables other than parameters are common among the program unit.
10 DEF f(x)=a*x^2+b*x*c 20 INPUT a,b,c 30 PRINT f(1),f(2) 40 END
On the above program, variables a, b, c in line 10 and variables a, b, c in line 20 are the same, respectively.
Define a function with no parameter
A function that have no parameter is written without parentheses.
10 DEF spot=INT(6*RND+1) 20 FOR i=1 TO 100 30 PRINT spot 40 NEXT i 50 END
The result of a DEF statement has the precision of over 16 digits on the decimal operation mode. （not rounded to 15 digits as on a LET statement）
Functions can not be re-defined during execution as on some interpreter dialect.