Cant Use my function that i 've created in Header file

I'm trying to use my function that i've created previously in Main.cpp and then i came up with the idea to include my function to my own header file named center.h . i'm not sure why i cant called my function in another .cpp file but i think there something i didn't do in my code

PS . this function used to align any text in the center of each row

center.h

center.cpp