you are on the right track.. all you need to do now.. is pass in your arrays instead of double constants...
void function(double my_array_1, double my_array_2)
//Use a 'for' loop here based array size
//assign the contents of one array into a 'temp' variable temp = array1[i];
//assign the back of one array.. into the beginning of the other one array1[i] = array2[j];
//assign the 'temp' variable to the back of the second array array2[j] = temp;
tip: you don't need to loop through the entire arrays.. you only need to loop 1/2 way through each array ( array_size / 2 )