While I did not flash a device to do a test run (I am sure it will work fine); This works perfectly fine for me (both as C and as C++). #include <stdio.h> #include <tinyexpr.h> #ifdef __cplusplus extern "C" #endif void app_main() { printf("%f\n", te_interp("5*5", 0)); /* Prints 25. */ } I suspect wh...