Like many who grew up in the 1980s, my first programming language experience was on BASIC (on the VIC-20, in my case) and although I haven't used it for 30 years I felt right at home.
The Wikipedia article defines three broad generations of BASIC
- Early versions on mainframes, 1964-1980
- Home computer ROM BASIC, 1980-1990
- More structured versions on PCs, 1990-date
MTS BASIC falls firmly in the first camp, with a limited number of keywords, restrictions on numbers and names of variables, but with support for matrix operations that was not present in later versions of the language.
The below is a quick look at the main features in MTS BASIC; see the Further Information section for more complete guides.
Each line of the program must start with a line number - note this is different from line numbers in MTS native files and only integers are allowed.
Full line comments can be introduced with
*. To add a comment that lasts until the end of the line you can use
/* (very confusing to C programmers!).
10 rem This is a comment 20 * This also 30 let x = 3 /* Line comment 40 let y = 4
Types and variables
10 let A = 1.23 20 let A1 = 3 30 let AA = "Hello world"
You can have arrays and matrices of numbers which can be indexed using
b(2,3). The size can be set using the
DIM statement but if not given they are size 10. Indices start at 0. The below will print 100.
10 dim a(2,2) 20 a(1,0) = 100 30 a(1,1) = 200 40 print a(1)
Strings are implemented as vectors of cells containing strings, so
AA is the same as
AA(0) and you can also access
INPUT will prompt for the user to enter a value which will be assigned to a variable;
, to control formatting.
10 input a, b 20 print a; b, (a+b)/2 : run ? 10 ? 20 10 20 15
OUT are like
GOTO x will jump unconditionally to line
x. Note you can't
GOTO a non-executable line like a comment. There is also a rather hairy computed
GOTO where they program will jump to a line based on the result of an expression.
10 goto 40 20 print "This will be printed second" 30 stop 40 print "This will be printed first" 45 let a=2 50 goto (60,60,20,60) a+1 60 print "This will not be printed"
IF .. THEN statement will calculate an expression and then either jump to another line or execute a statement. Note that there is no
10 let a = 5 20 if a > 1 then 40 30 print "This will not be printed" 40 if a <> 5 then: print "This will not be printed" 50 if a = 5 then: print "This will be printed"
Simple loops can be done with
NEXT with an optional
10 for i = 1 to 10 20 for j = 0 to 10 step 2 30 x = x + (i*j) 40 next j 50 next i 60 print x
GOSUB x will call a subroutine at line
x; execution will resume from the current line when a
RETURN statement is found.
It's possible to temporarily transfer execution to another program with
CALL or permanently transfer with
Simple functions can be defined with
DEF FNS(x)=x*x for a square function. Only one parameter is allowed and the function name can only be a single character A-Z.
STOP will end a program and
PAUSE will prompt the user for input before continuing.
BASIC comes with a number of library functions. Note that you have to assign results of these functions to variables rather than printing them directly - so in the example below I can't do
String operations include conversion to numbers (
STN) and back (
NTS) along with access to the surrounding environment such as
UID for user ID and
CLS for time of day.
10 let ss = cls() 20 print ss 30 let ss = uid() 40 print ss : run 0:59:02 ST01
Numeric functions include mathematical support functions like
Matrix and vector support is especially powerful, with the ability to enter, print and do matrix operations. The below will prompt for a 2x2 matrix, add it to its transpose and then print it.
10 dim x(2,2), y(2,2), z(2,2) 20 mat input x 30 mat let y = trn(x) 40 mat let z = x + y 50 mat print z : run ? 1,2 ? 3,4 2 5 5 8
There is also limited support to read and write files - but these are special data files attached to the BASIC environment rather than general MTS files.
And that's pretty much it for BASIC. In the next post we'll look at a larger example of a MTS BASIC program.
MTS Volume 10 offers a complete description of the BASIC language and environment.