Main.c:19:9: warning: incompatible pointer to integer conversion initializing 'int' with an expression of type 'void (int *)' [-Wint-conversion]
    int called = increment;
        ^        ~~~~~~~~~
Main.c:21:12: warning: incompatible pointer to integer conversion passing 'int *' to parameter of type 'int'; remove & [-Wint-conversion]
    caller(&x, called);
           ^~
Main.c:10:17: note: passing argument to parameter 'arg' here
void caller(int arg, void (*inc)(int)){
                ^
Main.c:21:16: warning: incompatible integer to pointer conversion passing 'int' to parameter of type 'void (*)(int)' [-Wint-conversion]
    caller(&x, called);
               ^~~~~~
Main.c:10:29: note: passing argument to parameter 'inc' here
void caller(int arg, void (*inc)(int)){
                            ^
3 warnings generated.