Hallo Tomas

1. You can't return an array from the function this way. It is valid inside the function only. One possible solution, add 'static' to the array defintion.

2. The valid array index is 0,...19 only, so the loop can't be
for (i = 0; i < 21; i++) but for (i = 0; i < 20; i++) only.
My preferred solution is a global defintion

#define ArrayElementCount(X) (sizeof(X)/sizeof(X[0]))

then be used for all arrays in the project, like

for (i = 0; i < ArrayElementCount(temperature_array); i++)

this way I can easily modify the array length, by just edit
ONE single place, the variable definition.

Best regards, Juergen