// Taken from https://github.com/kobalicek/mathpresso

mapthpresso.cpp

#include <mathpresso/mathpresso.h>
#include <stdio.h>

int main(int argc, char* argv[]) {
  mathpresso::Context ctx;
  mathpresso::Expression exp;

  // Initialize the context by adding MathPresso built-ins. Without this line
  // functions like round(), sin(), etc won't be available.
  ctx.addBuiltIns();

  // Let the context know the name of the variables we will refer to and
  // their positions in the data pointer. We will use an array of 3 doubles,
  // so index them by using `sizeof(double)`, like a normal C array.
  //
  // The `addVariable()` also contains a third parameter that describes
  // variable flags, use `kVariableRO` to make a certain variable read-only.
  ctx.addVariable("x", 0 * sizeof(double));
  ctx.addVariable("y", 1 * sizeof(double));
  ctx.addVariable("z", 2 * sizeof(double));

  // Compile the expression.
  //
  // The create parameters are:
  //   1. `mathpresso::Context&` - The expression's context / environment.
  //   2. `const char* body` - The expression body.
  //   3. `unsigned int` - Options, just pass `mathpresso::kNoOptions`.
  mathpresso::Error err = exp.compile(ctx, "(x*y) % z", mathpresso::kNoOptions);

  // Handle possible syntax or compilation error.
  if (err != mathpresso::kErrorOk) {
    printf("Expression Error: %u\n", err);
    return 1;
  }

  // To evaluate the expression you need to create the `data` to be passed
  // to the expression and initialize it. Every expression returns `double`,
  // to return more members simply use the passed `data`.
  double data[] = {
    1.2, // 'x' - available at data[0]
    3.8, // 'y' - available at data[1]
    1.3  // 'z' - available at data[2]
  };
  printf("Output: %f\n", exp.evaluate(data));

  return 0;
}