A simple lexer for mathematical expressions, implemented in ISO C11. The project is organised following common C project practices: public headers live under include/, reusable code is built as a static library, and the command-line demo is compiled as a thin frontend on top of the library.

math-expr-lexer/
├── CMakeLists.txt       # Build configuration
├── include/
│   └── math_expr/       # Public headers
├── src/
│   ├── app/             # Executable entry points
│   └── lexer/           # Library implementation files
├── config.h             # Project configuration stub
├── LICENSE              # Project license
└── README.md            # This document

Additional scaffolding folders such as bin/, build/, docs/, scripts/, lib/, and tests/ can be introduced as the project grows. They are not created by default to keep the repository clean when unused.

• ISO C compiler (gcc, clang, or MSVC`)
• CMake
• Make or another build tool supported by CMake

Create and enter the build directory:

mkdir -p build
cd build

Configure the project:

cmake ..

Build the targets:

cmake --build .

The executable will be generated at bin/math_expr_lexer (or with .exe on Windows).

From the project root after building:

./bin/math_expr_lexer "3 + 2 - 4 * 5 / sin(30)"

Example output:

Expression: 3 + 2 - 4 * 5 / sin(30)

Tokens:
NUMBER       -> 3          (value = 3)
SPACE        -> [space]
OPERATOR     -> +
...

Result: -35

The bundled evaluator understands common arithmetic operations, parentheses, and a handful of functions such as sin, cos, tan, sqrt, abs, log, and pow. Trigonometric functions expect the argument in degrees.

Client code should include math_expr/lexer.h, initialise a math_expr_token_array, and pass it to math_expr_lex_expression. Remember to clean up with math_expr_token_array_deinit when the token array is no longer needed.

#include "math_expr/lexer.h"

int main(void) {
    math_expr_token_array tokens;
    math_expr_token_array_init(&tokens);

    if (math_expr_lex_expression("2 * (x + 1)", &tokens) != 0) {
        return 1;
    }

    /* consume tokens->data here */

    math_expr_token_array_deinit(&tokens);
    return 0;
}

To remove build artefacts, delete the build/ and bin/ directories:

rm -rf build bin