In these cases data was set as `process_post_synch(window->owner, ctk_signal_keypress, (process_data_t)(size_t)c);` so it seems reasonable to cast "back" to `size_t`. Additionally the comparison can be limited to `char`. See i.e. calcc for reference:
```
if(ev == ctk_signal_keypress) {
if((char)(size_t)data >= '0' &&
(char)(size_t)data <= '9') {
```