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Introduction

Welcome here! This is MSX BASIC interpreter with some small changes (e.g. == instead of = for comparisons and improved error messages). You can try MSX BASIC online here.

Table of Contents

  1. Getting Started
  2. Numbers
  3. Math Functions
  4. Commands Reference
  5. Arrays
  6. Program Mode
  7. Tips and Tricks
  8. Contribute

Getting Started

This interpreter lets you run BASIC commands either immediately (immediate mode) or write programs with line numbers (program mode). You can type commands and see results right away!

Numbers

Numbers can be written in different formats:

  • Regular decimal: 42, 3.14
  • Hexadecimal (base 16): &H2A
  • Binary (base 2): &B101010
  • Octal (base 8): &O56226

Math Functions

Function What it does
SIN(x) Sine of x (radians)
COS(x) Cosine of x
TAN(x) Tangent of x
ARCSIN(x) Inverse sine (-1 to 1)
ARCCOS(x) Inverse cosine (-1 to 1)
ARCTAN(x) Inverse tangent
SQR(x) Square root
LOG(x) Base-10 logarithm
LN(x) Base-e logarithm
EXP(x) e to the power x
ABS(x) Absolute value
SGN(x) Sign (-1, 0, or 1)
INT(x) Integer part (truncates)
VAL(x) Convert string to number
RND Random number 0-1

Commands Reference

PRINT - Display Information

Show values on the screen:

PRINT "Hello World"
PRINT "The answer is "; 42
PRINT x + y
PRINT "Sum:"; a + b

Use semicolons ; to keep output on the same line. Without a final semicolon, PRINT adds a newline.

INPUT - Get User Input

Ask the user for information:

INPUT "What is your name? "; name
INPUT "Enter age: "; age
INPUT password

LET - Assign Values

Store values in variables:

LET x = 10
LET name = "Alice"
result = (a + b) * 2

IF ... THEN ... ELSE - Make Decisions

Control program flow:

IF x > 10 THEN PRINT "x is big"
IF score >= 90 THEN grade = "A" ELSE grade = "B"
IF a == b THEN PRINT "Equal" ELSE PRINT "Different"

FOR ... TO ... STEP ... NEXT - Loops

Repeat code multiple times:

FOR i = 1 TO 10
PRINT "Count: "; i
NEXT i

FOR i = 0 TO 100 STEP 10
PRINT i
NEXT

FOR i = 10 TO 1 STEP -1
PRINT "Countdown: "; i
NEXT

GOTO - Jump to Line

Move to a different line in your program:

10 PRINT "Infinite loop!"
20 GOTO 10

GOSUB ... RETURN - Subroutines

Call and return from subroutines:

10 GOSUB 100
20 PRINT "Back from subroutine"
30 END

100 PRINT "In subroutine"
110 RETURN

SLEEP - Pause Program

Wait for specified milliseconds:

PRINT "Wait 2 seconds..."
SLEEP 2000
PRINT "Done!"

CLS - Clear Screen

Clear the display:

CLS

REM - Comments

Add notes in your code (ignored by interpreter):

REM This is a comment
LET x = 42: REM This also works

END - Stop Program

Terminate program execution:

IF score < 0 THEN END

Arrays

Array Declaration (DIM Statement)

Declare arrays to store multiple values:

DIM array_name(size)
DIM arr1(10), arr2(20), arr3(5)
  • Use DIM keyword to declare arrays
  • Specify array name and size in parentheses
  • Multiple arrays can be declared in a single DIM statement, separated by commas
  • Array sizes must be positive integers
  • All elements are initialized to 0.0

Array Assignment and Access

Access and modify array elements:

LET array(index) = value
LET A(0) = 100
LET B(i) = A(i) + 1
PRINT array(index)
  • Use parentheses (index) to access array elements
  • Indices are 0-based (first element is at index 0)
  • Array indices must be numeric expressions (0 to size-1)
  • Bounds checking prevents accessing invalid indices

Array Usage Tips

  1. Declare all arrays at the beginning of your program
  2. Use consistent naming: scores(10), names(50), etc.
  3. Remember arrays are 0-indexed
  4. Use FOR loops to efficiently process array elements

Example: Array Processing

10 DIM values(10)
20 FOR i = 0 TO 9
30   LET values(i) = i * 10
40 NEXT
50 FOR i = 0 TO 9
60   PRINT values(i)
70 NEXT

Example: Statistics

10 DIM scores(5)
20 LET scores(0) = 85
30 LET scores(1) = 92
40 LET scores(2) = 78
50 LET scores(3) = 95
60 LET scores(4) = 88
70 LET sum = 0
80 FOR i = 0 TO 4
90   LET sum = sum + scores(i)
100 NEXT
110 LET average = sum / 5
120 PRINT "Sum: "; sum
130 PRINT "Average: "; average
140 END

Program Mode

Line Numbers

Create programs by adding line numbers:

10 PRINT "Hello"
20 INPUT "Enter number: "; n
30 IF n < 0 THEN END
40 PRINT "You entered: "; n
50 GOTO 20

Program Commands

Command What it does
LIST Show all program lines
RUN Execute the program
NEW Clear current program
LOAD "filename" Load program from file

Example:

NEW
10 PRINT "My Program"
20 FOR i = 1 TO 5
30 PRINT "Line "; i
40 NEXT i
RUN
LIST

Tips and Tricks

  1. Multiple statements on one line use colons ::
LET x = 5 : PRINT "x = "; x : LET y = x * 2
  1. String concatenation uses +:
full = "Hello" + " " + "World"

  1. Comparison operators: ==, <> (not equal), <, >, <=, >=

  2. Variable names can be longer than a single letter!

  3. Logical operators: AND, OR for combining conditions:

IF x > 0 AND x < 10 THEN PRINT "Between 0 and 10"
IF a == 1 OR b == 1 THEN PRINT "At least one is 1"

Contribute

If any errors occur or you want to add some more features then just fork and send PR or create an issue.