vb2c

vb2c compiles a unique dialect of BASIC, Very BASIC, to C.

Current Language Features

• Numerical variables
• Floating-point arithmetic
• Comparison operators
• If statements
• While loops
• Goto and labels
• User input
• Console output
• Comments
• Conditional includes
• Basic compile-time error checking

Usage

vb2c -s <path to source file> [-o <path to output file>]

If unspecified, the default output file is out.c in the current working directory.

The vbas file extension is recommended for Very BASIC source code, but it is by no means required.

Example

Very BASIC Source Code

# Compute the mean of a specified number of test scores

LET a = 0
WHILE a < 1 REPEAT
    PRINT "Enter number of scores: "
    INPUT a
ENDWHILE

LET b = 0
LET s =  0
PRINT "Enter one value at a time: "
WHILE b < a REPEAT
    INPUT c
    LET s = s + c
    LET b = b + 1
ENDWHILE

PRINT "Average: "
PRINT s / a

Generated C Code (After Autoformatting)

#include <stdio.h>
#include <stdlib.h>
int main(void)
{
    float a;
    float b;
    float s;
    float c;
    a = 0;
    while (a < 1)
    {
        printf("Enter number of scores: \n");
        if (scanf("%f", &a) == EOF)
        {
            printf("Error: Invalid input\n");
            exit(EXIT_FAILURE);
        }
    }
    b = 0;
    s = 0;
    printf("Enter one value at a time: \n");
    while (b < a)
    {
        if (scanf("%f", &c) == EOF)
        {
            printf("Error: Invalid input\n");
            exit(EXIT_FAILURE);
        }
        s = s + c;
        b = b + 1;
    }
    printf("Average: \n");
    printf("%.2f\n", s / a);
    return EXIT_SUCCESS;
}

Grammar Specification

The current Very BASIC grammar is defined by the following EBNF:

program ::= {statement}
statement ::= "PRINT" (expression | string) newline
    | "IF" comparison "THEN" newline {statement} "ENDIF" newline
    | "WHILE" comparison "REPEAT" newline {statement} "ENDWHILE" newline
    | "LABEL" ident newline
    | "GOTO" ident newline
    | "LET" ident "=" expression newline
    | "INPUT" ident newline
comparison ::= expression (("==" | "!=" | ">" | ">=" | "<" | "<=") expression)+
expression ::= term {( "-" | "+" ) term}
term ::= unary {( "/" | "*" ) unary}
unary ::= ["+" | "-"] primary
primary ::= number | ident
newline ::= "\n"+

Build Locally

Prerequisites

• C++20 compiler (tested with GCC and Clang)
• CMake 3.14+
• Clang-Format (optional)
• Clang-Tidy (optional)

Steps

1. Clone the project:

  git clone https://github.com/smercer10/vb2c.git

2. Navigate to the project directory:

  cd vb2c

3. Generate the build files:

  cmake -S . -B build

4. Build the project:

  cmake --build build

Running Tests

The project utilises the GoogleTest framework with CTest.

To execute the testcases, run the following command from the project root:

  cmake --build build --target test

Contributing

Contributions are always welcome!

See open issues for ways to get started.

Acknowledgements

The compiler design is based on the excellent blog series by Austin Henley.