SmallBASIC Guide

Statement: REM comment Adds explanatory text to a program listing. comment commentary text, ignored by BASIC. Instead of the keyword we can use the symbol ' or the #. The # can be used as remarks only if its in the first character of the line. Example:

' That text-line is just a few remarks
...
REM another comment
...
# one more comment

Statement: LET var = expr Assigns the value of an expression to a variable. The LET is optional.

var A valid variable name.
expr The value assigned to variable.

Example:

LET x = 4
x = 1               ' Without the LET keyword
z = "String data"   ' Assign string
...
DIM v(4)
z=v                 ' Assign array (z = clone of v)

Statement: CONST name = expr Declares a constant.

name An identifier that follows the rules for naming BASIC variables.
expr An expression consisting of literals, with or without operators, only.

Example:

CONST G = 6.67259E-11

Statement: DIM var([lower TO] upper [, ...]) [, ...] The DIM statement reserves space in computer's memory for arrays. The array will have (upper-lower)+1 elements. If the lower is not specified, and the OPTION BASE hasn't used, the arrays are starting from 0. Example:

REM One dimension array of 7 elements, starting from 0
DIM A(6)
...
REM One dimension array of 6 elements, starting from 1
DIM A(1 TO 6)
...
REM Three dimension array
DIM A(1 TO 6, 1 TO 4, 1 TO 8)
...
REM Allocating zero-length arrays:
DIM z()
...
IF LEN(Z)=0 THE APPEND Z, "The first element"

Statement: LABEL name Defines a label. A label is a mark at this position of the code. There are two kinds of labels, the 'numeric' and the 'alphanumeric'. 'Numeric' labels does not needed the keyword LABEL, but 'alphanumeric' does. Example:

1000 ? "Hello"
...
LABEL AlphaLabel: ? "Hello"
...
GOTO 1000
GOTO AlphaLabel

Statement: GOTO label Causes program execution to branch to a specified position (label).
Statement: GOSUB label Causes program execution to branch to the specified label; when the RETURN command is encountered, execution branches to the command immediately following the most recent GOSUB command.
Statement: RETURN 0 Execution branches to the command immediately following the most recent GOSUB command.

...
GOSUB my_routine
PRINT "RETURN sent me here"
...
LABEL my_routine
PRINT "I am in my routine"
RETURN

GOTO|GOSUB label1 [, ..., labelN] Causes BASIC to branch to one of a list of labels.

expr A numeric expression in the range 0 to 255. Upon execution of the ON...GOTO command (or ON...GOSUB), BASIC branches to the nth item in the list of labels that follows the keyword GOTO (or GOSUB).

Statement: FOR counter = start TO end [STEP incr] ... NEXT Begins the definition of a FOR/NEXT loop.

counter A numeric variable to be used as the loop counter.
start A numeric expression; the starting value of counter.
end A numeric expression; the ending value of counter.
incr A numeric expression; the value by which counter is incremented or decremented with each iteration of the loop. The default value is +1.

BASIC begins processing of the FOR/NEXT block by setting counter equal to start. Then, if 'incr' is positive and counter is not greater than end, the commands between the FOR and the NEXT are executed. When the NEXT is encountered, counter is increased by 'incr', and the process is repeated. Execution passes to the command following the NEXT if counter is greater than end. If increment is negative, execution of the FOR/NEXT loop is terminated whenever counter becomes less than end. FOR/NEXT loops may be nested to any level of complexity, but there must be a NEXT for each FOR. Example:

FOR C=1 TO 9
    PRINT C
NEXT

Statement: FOR element IN array ... NEXT Begins the definition of a FOR/NEXT loop.

element A variable to be used as the copy of the current element.
array An array expression

The commands-block will repeated for LEN(array) times. Each time the 'element' will holds the value of the current element of the array. FOR/NEXT loops may be nested to any level of complexity, but there must be a NEXT for each FOR. Example:

A=[1,2,3]
FOR E IN A
    PRINT E
NEXT
...
' This is the same with that
A=[1,2,3]
FOR I=LBOUND(A) TO UBOUND(A)
    E=A(I)
    PRINT E
NEXT

Statement: WHILE expr ... WEND Begins the definition of a WHILE/WEND loop.

expr An expression

BASIC starts by evaluating expression. If expression is non-zero (true), the next command is executed. If expression is zero (false), control passes to the first command following the next WEND command. When BASIC encounters the WEND command, it re-evaluates the expression parameter to the most recent WHILE. If that parameter is still non-zero (true), the process is repeated; otherwise, execution continues at the next command. WHILE/WEND loops may be nested to any level of complexity, but there must be a WEND for each WHILE. Example:

C=1
WHILE C<10
    PRINT C
    C=C+1
WEND
...
' This is the same with that
FOR C=1 TO 9
    PRINT C
NEXT

Statement: REPEAT ... UNTIL expr Begins the definition of a REPEAT/UNTIL loop.

expr An expression

BASIC starts executing the commands between the REPEAT and UNTIL commands. When BASIC encounters the UNTIL command, it evaluates the expression parameter. If that parameter is zero (false), the process will be repeated; otherwise, execution continues at the next command. REPEAT/UNTIL loops may be nested to any level of complexity, but there must be an UNTIL for each REPEAT. Example:

C=1
REPEAT
    PRINT C
    C=C+1
UNTIL C=10
...
' This is the same with that
FOR C=1 TO 9
    PRINT C
NEXT

Statement: IF ... Syntax:

IF expression1 [THEN]
    .
    . [commands]
    .
[ [ELSEIF | ELIF] expression2 [THEN]
    .
    . [commands]
    .
]
[ELSE
    .
    . [commands]
    .
]
 ENDIF | FI

Block-style IF. Causes BASIC to make a decision based on the value of an expression.

expression An expression; 0 is equivalent to FALSE, while all other values are equivalent to TRUE.
commands One or more commands.

Each expression in the IF/ELSEIF construct is tested in order. As soon as an expression is found to be TRUE, then its corresponding commands are executed. If no expressions are TRUE, then the commands following the ELSE keyword are executed. If ELSE is not specified, then execution continues with the command following the ENDIF. IF, ELSE, ELSEIF, and ENDIF must all be the first keywords on their respective lines. THEN is optional, but if its defined it must be the last keyword on its line; if anything other than a comment follows on the same line with THEN, BASIC thinks it's reading a single-line IF/THEN/ELSE construct. IF blocks may be nested. Example:

x=1
IF x=1 THEN
    PRINT "true"
ELSE
    PRINT "false"
ENDIF
...
' Alternate syntax:
x=1
IF x=1
    PRINT "true"
ELSE
    PRINT "false"
FI

Single-line IF. Syntax:

IF expression THEN [num-label]|[command] [ELSE [num-label]|[command]]

Causes BASIC to make a decision based on the value of an expression.

expression An expression; 0 is equivalent to FALSE, while all other values are equivalent to TRUE.
command Any legal command or a numeric label. If a number is specified, it is equivalent to a GOTO command with the specified numeric-label.

Example:

' Single-line IF
x=1
IF x=1 THEN PRINT "true" ELSE PRINT "false"
...
IF x=1 THEN 1000
...
1000 PRINT "true"

Function: IF (expression, true-value, false-value) Returns a value based on the value of an expression. Example:

x=0
PRINT IF(x<>0,"true","false") : REM prints false

Statement: END [error]
Statement: STOP [error] Terminates execution of a program, closes all files opened by the program, and returns control to the operating system.

error A numeric expression.

The error is the value which will returned to operating system; if its not specified the BASIC will return 0. DOS/Windows, The 'error' value is very well known as ERRORLEVEL value.
Statement: RESTORE label Specifies the position of the next data to be read.

label A valid label.

Command: READ var[, var ...] Assigns values in DATA items to specified variables.

var Any variable.

Unless a RESTORE command is executed, BASIC moves to the next DATA item with each READ assignment. If BASIC runs out of DATA items to READ, an run-time error occurs. Example:

FOR c=1 TO 6
    READ x
    PRINT x
NEXT
...
DATA "a,b,c", 2
DATA 3, 4
DATA "fifth", 6

Statement: DATA constant1 [,constant2]... Stores one or more constants, of any type, for subsequent access via READ command. DATA commands are non-executable statements that supply a stream of data constants for use by READ commands. All the items supplied by all the DATA commands in a program make up one continuous "string" of information that is accessed in order by your program's READ commands. Example:

RESTORE MyDataBlock
FOR I=1 TO 3
    READ v
    PRINT v
NEXT
END
...
LABEL MyDataBlock
DATA 1,2,3

Statement: ERASE var[, var[, ... var]]

var Any variable.

De-allocates the memory used by the specified arrays or variables. After that these variables turned to simple integers with zero value. Example:

DIM x(100)
...
PRINT FRE(0)
ERASE x
PRINT FRE(0)
PRINT x(1):REM ERROR

Statement: EXIT [FOR|LOOP|SUB|FUNC] Exits a multiline function definition, a loop, or a subprogram. By default (if no parameter is specified) exits from last command block (loop, for-loop or routine).

FOR Exit from the last FOR-NEXT loop
LOOP Exit from the last WHILE-WEND or REPEAT-UNTIL loop
SUB Return from the current routine
FUNC Return from the current function

Function: LEN (x)

x Any variable.

If x is a string, returns the length of the string. If x is an array, returns the number of the elements. If x is an number, returns the length of the STR(x).
Function: EMPTY (x)

x Any variable.

If x is a string, returns true if the len(x) is 0. If x is an integer or a real returns true if the x = 0. If x is an array, returns true if x is a zero-length array (array without elements).
Function: ISARRAY (x)

x Any variable.

Returns true if the x is an array.
Function: ISNUMBER (x)

x Any variable.

Returns true if the x is a number (or it can be converted to a number) Example:

? ISNUMBER(12)          :REM true
? ISNUMBER("12")        :REM true
? ISNUMBER("12E+2")     :REM true
? ISNUMBER("abc")       :REM false
? ISNUMBER("1+2")       :REM false
? ISNUMBER("int(2.4)")  :REM false

Function: ISSTRING (x)

x Any variable.

Returns true if the x is a string (and cannot be converted to a number) Example:

? ISSTRING(12)      :REM false
? ISSTRING("12")    :REM false
? ISSTRING("12E+2") :REM false
? ISSTRING("abc")   :REM true
? ISSTRING("1+2")   :REM true

Command: APPEND a, val [, val [, ...]]

a An array-variable.
val Any value or expression

Inserts the values at the end of the specified array.
Command: INSERT a, idx, val [, val [, ...]]]

a An array-variable.
idx Position in the array.
val Any value or expression.

Inserts the values to the specified array at the position idx.
Command: DELETE a, idx [, count]

a An array-variable.
idx Position in the array.
count The number of the elements to be deleted.

Deletes 'count' elements at position 'idx' of array A