BasicPlusPlus

• Just another BASIC-like language written in C++
• C++ code documentation can be found in DEV_DOCS.md directory
• Available at: https://github.com/gamecraftCZ/BasicPlusPlus

Usage

basicplusplus <file>

Example code

REM Personalised welcome script

INPUT "Whats your name: ", name
INPUT "How old are you: ", age
TONUM age

IF age < 12 THEN
  PRINT "Hi kid!"
ELSE
  PRINT "Welcome " + name
END

• More examples in examples/ directory

Variable names

• Can contain only english alphabet and underscore a-zA-Z_
• Must not collide with builtin keywords
• Case sensitive

Variable types

• String: variable length UTF-8 string
• Number: IEEE double-precision floating point number (64 bit)
• Boolean: true / false

Variable assigment

Variable are declared and assigned using LET keyword

• eg. LET num = 14

• eg. LET VarOne = "Age: " + 14

• You must use let even when assigning to already existing variable.

• There is no such value as null. Every variable must have a value.

Operations with types

• Number

  • Comparing <,>,<=,>=,==,<>

    • <number> OP <number> -> <boolean>
    • eg. 7 > 5 -> true

  • Arithmetic +,-,*,/

    • <number> OP <number> -> <number>
    • eg. 7 / 2 -> 3.5
    • DivisionByZero runtime error may occur.

  • Negation -

    • - <number> -> <number>
    • eg. -7 -> -7

• String

  • Joining +

    • <string> + <string> -> <string>
    • <string> + <number> -> <string>
    • <string> + <boolean> -> <string>
    • <number> + <string> -> <string>
    • <boolean> + <string> -> <string>
    • eg. "I am from" + "Pilsen" -> "I am from Pilsen"
    • eg. "I am " + 7 + "years old." -> "I am 7 years old."
    • eg. "This statement is " + True -> "This statement is TRUE"

  • Comparing ==, <>

    • <string> OP <string> -> <boolean>
    • eg. "Hello" == "hello" -> false
    • Comparing is case sensitive

• Boolean

  • Negation NOT

    • NOT <boolean> -> <boolean>
    • eg. NOT true -> false

  • Logic operators AND,OR

    • <boolean> OP <boolean> -> <boolean>
    • eg. false OR 1 > 0 AND true -> true

Operator precedence

• You can group expressions using ( and )
• Precedence is from highest to lowest
  1. () - grouping
  2. - - negation
  3. /,*
  4. -,+
  5. <,>,<=,>=,==,<>
  6. NOT
  7. AND
  8. OR

Language functionality

• Keywords are case-insensitive

• There is no such value as null. Every variable must have a value.

Input / Output

• PRINT <expr>
  • Evaluates and prints expr to stdout with new line at the end
  • <expr> can be string, number, boolean
  • number is printed to two decimal places if decimal, otherwise it gets printed without decimal places if whole.
  • eg. PRINT "Age: " + 7
• INPUT <expr>, var
  • Evaluates and prints expr to stdout and reads user input to variable var
  • <expr> can be string, number, boolean
  • eg. INPUT "Age: ", age

Control flow

• IF

  • Executes expr, if result is true, execute expressions in then_branch, else execute expressions in else_branch if exists.
  • Else branch is optional
  • Branches can contain multiple expressions
  • Usage:

  IF expr THEN
    ...then_branch...
  (ELSE
    ...else_branch...)
  END

  • eg.

  IF 5 < 7 THEN
    PRINT "Hello"
    PRINT "Low number"
  ELSE
    PRINT "Else never occures"
  END

• WHILE

  • Execute code until expr evaluates to true
  • Usage:

  WHILE expr DO
    code
  END 

  • eg.

  LET i = 0
  WHILE i < 10 DO
    PRINT "Hello for " + i + " time."
    LET i = i + 1
  END

• BREAK

  • Stops execution of code and exits the closest WHILE loop.
  • LoopControlOutsideLoop error may occur if not inside a loop.

• CONTINUE

  • Stops execution of code and continues at the beginning of the closest WHILE loop.
  • LoopControlOutsideLoop error may occur if not inside a loop.

Other

• REM comment

  • Comment. Anything after REM on that line is ignored.

• TONUM var(, out_var)

  • Converts var to number and saves the result to out_var
  • If only var is defined, output is saved back to var
  • InvalidNumberFormat error may occur if conversion failed

• TOSTR var(, out_var)

  • Converts var to string and saves the result to out_var
  • If only var is defined, output is saved back to var

• RND var, lowerBound, upperBound

  • Generates random integer in range [lowerBound, upperBound) including lowerBound, excluding upperBound.
  • Stores result to var

Runtime errors

If error occur, execution of code stops and error message is printed to stderr.

• DivisionByZero = tried to divide by 0
• LoopControlOutsideLoop = using continue or break outside of loop body
• InvalidNumberFormat = parsing string that is not a number using TONUM
• VariableNotDeclared = using variable that was not declared before
• ConditionNotBoolean = condition in IF or WHILE evaluated to non boolean value